Any applications to protect server?

Hello. I Have been running a Bukkit server for a couple months now, and I've been concerned about security.
So I was wondering if anyone knows of some program/plugin that gives extra security. I'm not very concerned about things like force op, and things that do stuff in-game. More like hacking in and taking control of my PC.
I'm running the 1.6.4 Dev. build
Thanks!
Creepy