I really cant help with what might have happened, it may well have been RedHat's update that cuased the problem, but very hard to say.

If you system has been on the internet unprotected (ie firewall) for any length of time you may have been hacked, specially if you have broadband access and a static IP ...

You may want to check out chkrootkit that can be obtained from http://www.chkrootkit.org ... this small script will, when run, check you system for common rootkits currently installed and used by crackers.

If you are still in doubt, nebulus200's suggestion of pulling the machine off the internet and rebuilding is a sound suggestion, .... fresh install, update, harden then get it back online.

Good luck.