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Authentication Key Problems

You will receive an Authentication Key when you purchase the full game.
An authentication key looks something like this:

DEFCON Shows "Key Unknown" when I try to authenticate
Your key is fine, but you have a problem with your networking. In this state you can play a single player game, or LAN game with players with different keys. You must be connected to the internet for DEFCON to be able to authenticate your key and allow you to play against other on-line gamers. Troubleshooting for network problems can be found here.
I have lost my Key
In August 2012 we changed the method we use to distribute our games. You'll need to contact us and we'll grant you access to the new store. Please note that it really speeds things up of you can tell us the email address used when you ordered the game.
I'm having trouble with the Steam version
Steam uses a slightly different key authentication system.
Please visit our Steam Support page.
My key has been Banned
If you find your key has been banned it means our system has detected multiple uses of your Key from many different IPs, suggesting your key is being used by many people. In order to fix this problem we must issue you a new key. You must contact us in order to resolve this issue.
I have a Full-Game key but don't know what to do with it
Click here for instructions on upgrading the Defcon Client to the full game.