Sorry if this has been posted somewhere before, I did a quick search but didn't see it anywhere.
I found this nice little tool that searches your *nix system for the possibility of a rootkit infection. It is similar to chkrootkit but it doesn't seem to throw up the false positives that chkrootkit does.
Rootkit Hunter is very easy to install and and has a nice interactive run feature on the commandline. While no tool is perfect it will scan the system for many of the common rootkits.
Just another one to drop into your *nix arsenal
For more info here is the official site;
rkhunter - http://www.rootkit.nl
... and a bit of a story about it at NewsForge can be found here