VIRUS PROGRAMMING
Everybody is scared of computer ‘virus’ as it does harmful actions on our computer. But
when we look into the virus programming, we may certainly come out with the conclusion that it requires intelligence to code a virus.
Logic
It is easy to mess-up the right program. For example, if you remove even a single byte
from an EXE file, that EXE file won’t be usable! Virus program don’t have any specific rules.
But it’s a common practice to include ‘signatures’ by virus creators. The main idea is to force the innocent user to run the programs. So certain viruses come along with so called ‘programmer utilities’ or ‘free tools’. Another thing is, it is easy to hang-up a working system using some ‘bad’interrupts.
Viruses use this logic too! TSR viruses
When TSR got its popularity, crackers started using TSR concepts for virus
programming. There was a time when people who knew TSR started writing their own TSR viruses. But when Windows operating system was introduced, TSR viruses lost their “popularity”.
I have written the following program. This is actually a TSR virus. It is not much
harmful; it just changes the attribute (color) byte of the existing characters present on screen.
#ifndef __SMALL__
#error Compile with Small memory model #else
#include
int i = 1;
char far *Vid_RAM = (char far *)0xb8000000; void interrupt (*Int9)( void );
void interrupt MyInt9( void );
void interrupt MyInt9( void )
{
*( Vid_RAM + i ) = i;
if ( i>4000 )
i = 1;
else
i += 2;
(*Int9)( );
} /*--interrupt MyInt9-----*/
int main(void)
{
Int9 = getvect( 9 );
setvect( 9, MyInt9 );
keep( 0, 500 );
return(0);
} /*--main( )----*/
#endif
