Assembly
Program to prevent CTRL+ALT+DEL from restarting the system
Program to prevent CTRL+ALT+DEL from restarting the system To use it just type, from the dos prompt: MASM NOCAD; (of course you need MASM) LINK NOCAD; (and of course you need a linker) NOCAD If you type NOCAD once it has been loaded, it will tell you so. I've used it with DOS 3.30, but it works just as well under DOS 2.00 and above. If you have any comment of any kind please let me know. And have a nice new decade everybody. cut here: ************************************************************ page 255,132 ;just to get a nice list file comment : Program to prevent CTRL+ALT+DEL from restarting the system WARNING: Once loaded, you only have three choices: 1) Turn power off 2) Use a reset button (not all the machines have one) 3) Generate INT 19h WARNING: If you have a program that uses INT 0CDh, change this value in the equates line below to the number of a not used INT. This method is used because there are too many programs that hook INT 9 Vector and we can't be sure it always points to the end of our notice (and start of our ISR). NOTE: For memory references i use parentheses instead of square brackets because of ASCII-EBCDIC translations. It works the same under Microsoft's MASM 4.0 NOTE: NOCAD won't work if you press CTRL+ALT+DEL from a program that hooked to INT 9 before NOCAD (example: SideKick). Solution: Load NOCAD before everything else. ctrl equ 0100b ;bit map for ctrl key alt equ 1000b ;bit map for alt key free_vector equ 0CDh ;vector used to prevent double loading ;change it if your system uses INT 0CDh nocad segment byte 'CODE' assume cs:nocad, ds:msgs, es:nothing, ss:stack Copyright db 'Antonio Quezada-Duarte ITESM ISC 296641 Monterrey ' db 'Nuevo Leon MEXICO' Cright_Len equ $-Offset Copyright new_int_9h proc near push ax push ds ;save registers xor ax,ax mov ds,ax ;point DS to BIOS data area ;well, actually BIOS data area ;starts at 0040:0000, but ; XOR AX,AX is faster than MOV AX,40h mov al,ds:(417h) ;get keyboard flags and al,ctrl+alt ;clear non relevant bits cmp al,ctrl+alt ;compare to our map jne go_ahead ;NO CTRL+ALT keys pressed and byte ptr ds:(417h),not alt ;CTRL+ALT pressed ;clear ALT key bit to simulate ;ALT key is not pressed go_ahead: pushf ;old ISR returns with IRET COMMENT : The Following code stands for CALL OLD_INT_9 Where OLD_INT_9 is a FAR PROC this is faster than having the address of OLD_INT_9 stored in memory and doing a CALL CS:(OLD_INT_9) : DB 9Ah OLD_INT_9_OFS DW 0 OLD_INT_9_SEG DW 0 ;call old INT 9 ISR pop ds pop ax ;restore registers iret ;return to caller new_int_9h endp begin proc near push es ;save psp base address mov dx,seg msgs mov ds,dx mov dx,offset msg_0 mov ah,9 int 21h mov ax,3500h + free_vector int 21h mov di,bx ;ES:DI ===> start of INT 0CDh ISR mov si,offset copyright mov ax,cs mov ds,ax ;DS:SI ===> THIS code copyright notice mov cx,cright_len cld repe cmpsb ;compare je loaded ;if equal then already loaded mov ax,2500h + free_vector mov dx,cs mov ds,dx mov dx,offset copyright int 21h ;point free_vector INT vector to ;our copyright notice mov ax,3509h int 21h ;get pointer to INT 9 ISR mov cs:old_int_9_ofs,bx mov cs:old_int_9_seg,es ;put it IN the new INT 9 ISR mov ax,2509h mov dx,offset new_int_9h push cs pop ds int 21h ;point INT 9 vector to our ISR mov dx,seg msgs mov ds,dx mov dx,offset msg_1 mov ah,9 int 21h ;print loaded msg pop ds ;get saved psp base address mov es,ds:(2Ch) mov ah,49h int 21h ;free environment's memory ;assume no error mov dx,offset begin ;everything up to BEGIN add dx,10Fh ;and all the bytes needed to mov cl,4 ;make a full paragraph ... shr dx,cl mov ax,3100h ;... stay resident int 21h ;and return exit code = 0 loaded: pop ax ;get psp address out of stack ;any register will do mov dx,seg msgs mov ds,dx ;point DS to our data area mov dx,offset msg_2 mov ah,9 int 21h ;print already loaded msg mov ax,4C01h int 21h ;terminate with exit code = 1 begin endp nocad ends msgs segment word 'DATA' msg_0 db 10,13,'NOCAD: Prevent CTRL+ALT+DEL from restarting the ' db 'system',10,13,'Author: Antonio Quezada-Duarte',10,13,'$' msg_1 db 10,13,'NOCAD Loaded OK.',10,13,'$' msg_2 db 10,13,'NOCAD Already Loaded.',10,13,'$' msgs ends stack segment para stack 'STACK' dw 1024 dup (?) stack ends end begin
Program to prevent CTRL+ALT+DEL from restarting the system
