how to make a programme modify itself on running in c

Question

i have a simple programme that shuts down a computer but it always gets detected as a virus when i share the exe file so i was wondering if i could make the programme treat a part of the code like a comment until it is run. for example before it is run

#include <stdio.h>
#include <stdlib.h>

int main()
{
    if(programme is running)
    {remove /* on line 8;}
    /*system("C:\\WINDOWS\\System32\\shutdown /s");*/
    return 0;
}

i tried storing it in a zip but it still gets detected as a virus. that is why i was looking for a way to make it self modifying so it can bypass windows security

Answer 1

What you are asking cannot be done. During compilation, all comments are disregarded, so the compiled binary code will have no trace of the comments.

Within the specifications of the C language, it is not possible to change the executable code, only modifiable data.

Hence, unless you will be doing low-level tricks (possibly outdated) you are limited to modifying the program data.

You could, for example, store the system command string "C:\\WINDOWS\\System32\\shutdown /s" in an "encrypted" string:

  char command[] = "D;]XJOEPXT]Tztufn43]tivuepxo!0t";

and then have the code modify it into the real command before running it. In this case:

   for(unsigned i = 0; i < sizeof(command)-1; i++) command[i] = command[i] - 1;
   system(command);

However, as others have commented, this is unlikely to make a difference in your underlying problem of the program being treated as a threat.

I would guess that making a truly self-modifying program makes it more - and not less - likely that the OS or anti-malware monitoring will see the program as a threat.