If you have decided to use Linux or another Unix-like operating system for your dedicated server, you probably factored in security into your consideration. Linux, BSD, and similar OSes are renowned for their inherent security features. Nevertheless, is still important to be diligent and make sure your server is as secure as possible. A unprotected Linux server can fall victim to security flaws just as easily as any other. This is especially true for servers connected to the Internet.
There is unfortunately no single security tool that will make Linux rock solid for you, but with the right combination of free and open source tools you can find online, you can make your server virtually impenetrable.