Steambans

[Dirtynap]

I would suggest using Steambans it works great.

All you need to do is register over at www.steambans.com

Then submit a team based on your game servers. You can join an exsiting team if you wish to save yourself some hassle.
Once approved you can download the files and install them. Its very simple.

You then add your license key to your config and restart thats it.
Works great.

Here is the how 2 on how to protect your server/