re: exploits
I've found, from my experience and that of several others is that RH versions 6.2 - 7.0 were big jucy targets for hackers. I can't speak for anything later than those versions. Mine was constantly being taken down. The only thing I ever did that stopped it was run Bastile (a hardening script designed for Redhat, I highly recommend it) and that took care of the issue as far as I could tell.