At the request of developer Unknown Worlds, Valve has deactivated 1,341 Steam keys for multiplayer shooter Natural Selection 2 that were purchased through a scam off the developer's website, according to the developer's blog.
According the post, some Natural Selection 2 players who had no previous issues with the game began receiving "Buy Again" messages when they tried to log in. The keys were purchased with credit cards using a "charge-back" mechanism that allowed the purchaser to dispute the charges. The developer never received payment for these games and lost $45 for each purchase, the price of the game plus a $22 fee, resulting in $30,000 in charges.
Unknown Worlds called the incident a "prime example" of the need to be alert when purchasing discount Steam keys from third parties. The developer advised affected buyers to contact the sites they purchased from for a full refund.
"We don't know how exactly these sites obtain their Steam keys," the developer wrote. "It seems likely that they were originally obtained from our store using stolen credit card information. Keys were then sold through a handful of questionable sites to people using legitimate credit cards. The owner of the stolen credit card ultimately disputed the charge and we lost the sale."
Natural Selection 2 can still be purchased officially through Steam and Unknown Worlds' website via the Humble Bundle store. The developer has provided a list of legitimate outlets for buying the game here, and will update the list as more places are approved.