[quote name='sunghost']Valve isn't going to automatically remove any of the keys from accounts. I don't think there's any way for the dev to distinguish legit keys from the exploited ones. If you activated an exploited key, you'd have to contact Valve's support to get it removed, sadly.. It's a lot of hassle.[/QUOTE]
Not always true. It depends on the game exploited and if the publisher/the party it was exploited from takes action. Stuff like Dirt 3 and other big exploited codes have been pulled from people's accounts pretty quickly. But again, it depends on who takes action. As far as I know, none of the many exploited IGN Prime keys have been revoked, as an example. Basically, if you're going to use a potentially exploited key, you've got to just be aware of the fact that there's a chance it could vanish later.