Testing the security of your system is important, but don't let a successful test lull you into a false sense of security. Just because these testing tools don't find a hole is no guarantee that someone with knowledge and imagination -- and a whole lot of time on their hands -- will also fail.

We already mentioned nmap and netcat for testing network security. It is also a good idea to check for weak passwords, especially if your system has multiple users. There are many tools available, such as the ones we've put into Resources at the end of this tutorial.