Personal Firewall Software protects monitored user from malicious programs, like Spy software and Trojan horses, by allowing him to control his computer's Internet traffic and how applications access the Internet. When any application on monitored computer tries to access the Internet, personal firewall makes sure it has user's permission first. This lets monitored user ensure that a rogue program will not sneak his important data out onto the Internet. Personal Firewall Software is very affective security tool and used by most of computer users today.