Unix: Rootkit detection and prevention

You could have a rootkit infection right now and be totally unaware. One of the key goals of a rootkit is, after all, to go undetected. If the rootkit is hiding files, processes, logins, etc., how would you know? If you can't see it, how would you remove it?

Story added 10. March 2013, content source with full text you can find at link above.