We fell victim to an exploit, not going to say what, about 3-4 weeks ago. No matter how SECURE of a $P455W0RD# you use it can be BYPASSED, not HACKED. Doing some homework and hunting. Here is what we found to work much better than anything for Protecting your server(s).
Requires SourceMOD (Highly recommended even for VAC enabled servers because they are not 100% protected from 'script' hackers).
For Extra Protection:
With these plug-ins and addons, your servers will be more than better off protected. ServSecurity PREVENTS changes to key files like Client.txt files, server.cfg, etc. without proper access (password). If changes are made to these files without proper access, the server kicks and bans the player and the file is reverted back. That is, IF they can get by KAC first. So far no one has been able to do so. But better to be SAFE then SORRY.
Hope this helps!
NOTE: Version may change after this posting, but versions stated in this writing are current at the time of entry.