I think a lot of games are using the Software Passport / Armadillo-System. I have implemented it in Psychoballs for the BigFishGames-Version. It was very easy. You can check out http://siliconrealms.com/index.shtml for more information.
Check also out the following threads:
http://forums.indiegamer.com/showthread.php?t=2009
http://forums.indiegamer.com/showthread.php?t=1844


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