Moral of this story: Only buy videogame keys from legitimate sources.
Credit card scams are a headache, not only for customers, but also the merchants who were unfortunate enough to charge the credit card in the first place. Credit card scam victims can simply (or maybe not so simply) ask their banks to issue chargebacks, forcing merchants to eat the costs. For videogame publishers, who've been on the receiving end of a chargeback, eating the costs of a chargeback, though painful, aren't too devastating. However, for an indie developer that isn't working on a budget of millions of dollars, chargebacks can be a bit of a problem.
Unknown Worlds Entertainment, the developers behind Natural Selection 2, was out $30,000 after it was discovered that 1,341 Steam keys of the game were purchased illegally with stolen credit cards. The real credit card owners, seeing the fraudulent charges, issued chargebacks for the keys.
Apparently, someone had used the stolen credit cards to purchase these keys off the Unknown Worlds store and then sold them to third parties at a discount. For now, Unknown Worlds has closed its store, though Natural Selection 2 keys are still purchasable via Steam.
Unknown Worlds has stated that any users who were apart of the scam should contact them for a refund, though it seems unlikely that the developer would refund money to users who didn't buy from a legitimate source in the first place.