That would set everyone's firewalls off! If you're pinging each IP to see if it's running the program, it would be classed as a 'hack attempt' by most firewalls. Plus the majority of people's IPs are dynamic so they change every time you reconnect to the internet, so the list would get outdated in a matter of hours, I'm afraid.

Although it seems a good idea, it's impractical, and could frighten some users when their firewalls go bezerk saying there's someone hacking into their computer!