While Tom's comments are very generous, I've never written any security related articles concerning Linux system administration. I'm just not qualified to do so. The security hardening measures I take are mundane things that anyone with "Linux system administration" on their resume would be doing anyhow (turn of remote services like rsh, use ssh, dump sendmail, examining system on a regular basis with a vulnerability assessment utility like Nessus, shutting off unnecessary services, etc.).
My own personal opinion: your average cracker is probably more interested in finding some vulnerable Wintel box to host some clandestine activities and isn't going to try busting into moderately secure box. Crackers going for glory are probably more interested in hacking some government web site or major portal. I'm guessing that by doing the basics and plugging up the most egregious holes, you're probably safer than 95% (maybe more) of all computers on the 'net.
The only worthwhile thing I ever wrote about Linux was basic Red Hat Linux 5.2 installation guide in autumn 1998, but that article is now obsolete and useless.
David, I suggest you work off of Jon Griffin's notes and some of the better security guides now available on the 'net.
