SELinux enforces the idea that programs should be limited in what files they can access and what actions they can take. However, by default it is turned off under RHEL / CentOS 5.x server? How do I turn it on?
The best protection against vulnerable software is running less software. How do I find out which services are enabled at Boot under CentOS / RHEL / Fedora Linux? How do I disable software which is not needed?