Other tips are not to have "subadmins" or give out your password or post it online anywhere. Most "hacking attempts" turn out to be untrustworthy or disaffected former admins screwing around (consider they could give out that information to anyone they wished).
If you think your admin password may have been compromised... CHANGE IT immediately. Another is to use a name other than "server.cfg" for your config file.
If you botch entering your password logging in, a person could see your password attempt in the chat log too, so make sure you get it right (or enter it before you get into the game, via the save password feature in JO/JKA's in-game browers, or Qtracker, etc).
Another issue is that stuff like Killtrackers and mods may have their own vulnerabilities. Use at your own risk. If you think there's some kind of security exploit in them, contact the maker of this unofficial addon and see if they can fix it.