Shaun Savage, a Linux security developer, turned to SELinux because it's well-supported.

"I wanted to use secure Linux because the projects I work on require ultra-security, and it's better supported," Savage said. "The NSA is behind it and they have more money."

"In my opinion, most servers should have SELinux on them because if any exploits are found -- or even if you don't know about (problems) -- it protects the system because it limits access," Savage said.

One downside is that even for experienced security gurus, SELinux can be puzzling.

Savage says: "Unless you know security, it's very difficult. Unless you've ever worked in multi-level security, I'd say don't even attempt to incorporate because of the terminology it uses. To most people it's gobbledygook. Most people can't understand it. If you don't know about security, it's not a good thing to learn."

A Red Hat version of SELinux is available at sourceforge.net.

Open-source software is a generic term applied to programs for which the source code is available -- but it may still cost money. Free software is a subset of open-source software and generally means that the software is available for use at no cost, subject to license agreements like the GNU General Public License. The Linux operating system, sometimes called the GNU Linux operating system, is free software.