Unknown Worlds is warning players about the dangers of purchasing discounted Steam keys after it had to cut off access to Natural Selection 2 for 1,341 players. The company recently discovered all of the keys were purchased from its online store using stolen credit cards. When the owners of those credit cards reported the charges, they also initiated a charge back. In the end, Unknown Worlds suffered $30,000 in damages made up of lost sales ($25) and fees ($22) associated with the charge backs.
The sad thing is the actual thieves are the only ones who aren’t suffering from any inconveniences. You see, the thieves purchased the Steam keys legitimately from Unknown Worlds using money that wasn’t theirs. They then re-sold those keys to other websites presumably at a discount. The thieves made a pure profit from their wrongdoings. On the other side, the players who thought they were buying legit keys can no longer access Natural Selection 2. Unknown Worlds suggested players contact the seller of the keys to get a refund, but they may not get anything for their troubles.
Natural Selection 2 is only officially available from Steam and directly from Unknown Worlds. You should question the legitimacy of keys that are sold anywhere else other than those two sites.
Source [Unknown Worlds]