K4SCREEN.asm

;  830 bytes 16-bit DOS patch.

; \masm32\bin\ml /c K4SCREEN.asm
; \masm32\bin\link16 K4SCREEN.obj;

.MODEL  small
.STACK 500h
.DATA
.CODE
PatchL         EQU 6
Buffer         Db  PatchL Dup(1)
handle   dw ?
intro    db "The Penguins Little Crack Patch",0dh,0ah,"For 4screens$" ;<---- Insert program name here

FileName db "4screens.EXE",0 ;<------- Filename to be patched
notfound db 0dh,0ah,"File not found!  Make sure Crack Patch is in program directory.$"
cracked  db 0dh,0ah,"File successfully patched. Enjoy!$"
Cant     db 0dh,0ah,"Can't write to file.$"
Done     db "File has been made.$"
String   db 085h,0 ;<------------- Byte e.g "85" to be patched

START:
mov     ax,cs
mov     ds,ax
mov     dx,offset intro ;<-------point to the time prompt
mov     ah,9 ;<------------------DOS: print string
int     21h
jmp openfile

openfile:

mov     ax,cs
mov     ds,ax
mov     ax,3d02h
mov     dx,offset FileName
int     21h
mov     handle,ax
cmp     ax,02h
je      filedontexist
jmp     write

filedontexist:
mov     ax,cs
mov     ds,ax
mov     dx,offset notfound
mov     ah,9 ;<------------------DOS: print string
int     21h ;<-------------------Display the time prompt
jmp exit

Write:
mov     bx,handle
mov     cx,0000h
mov     dx,07D6h ;<------------- Insert offset e.g "07d6" you want to Patch
mov ax,4200h
int     21h

mov     cx,patchl
mov     dx,offset String
mov     ah,40h
mov     cx,01h
int     21h
mov     ax,cs
mov     ds,ax
mov     dx,offset cracked
mov     ah,9 ;<------------------DOS: print string
int     21h ;<-------------------Display the time prompt
jmp exit

Exit:
mov     ah,3eh
int     21h
mov     ax,4c00h
int     21h
END START