"The glamorous new kids in the Linux security parade are
SELinux, AppArmor, and all manner of virtualization technologies.
(Though it is being discovered that virtual machines, just like
chroot jails, aren't all that difficult to break out of, so don't
count on them for strong security.)
"But don't overlook the reliable, helpful old-timer Bastille
Linux. Bastille Linux is both a batch of Perl scripts that lead you
through hardening your Linux system, and an educational tool. I
recommend running it just to get a grounding in basic security
measures--the newfangled things are nice, but the basics are still
important and valuable..."