Remember Prey, 3D Realms and Human Head Studio's 2006 first person shooter? Well, thanks to its discounting on Steam as part of their holiday sale, the digital distribution service has actually run out of keys for the game, effectively selling out, even though there is no physical media involved. Steam have confirmed that they are trying to acquire more keys and bring the deal back, but in the meantime, publisher 2K Games have consented to offer a discount on BioShock as an alternative.