The December 7 World of Warcraft expansion, Cataclysm, set a new record for PC games by selling over 3.3 million copies in the first 24 hours after its midnight release.
Cataclysm provides players of the subscription-based online game World of Warcraft with extra content: areas to explore, quests to complete, monsters to overcome and characters to play as.
The previous record was held by the WoW's November 2008 expansion, Wrath of the Lich King, which shifted 2.8 million upon its debut.
The figure, based on Activision Blizzard's company records and reports from key distribution partners, eclipses StarCraft II's 1.5 million from July 2010, which at that time had been the biggest PC game launch of the year.
Other big PC games of the last few months include the historical strategy game
Civilization V, the post-apocalyptic adventure
Fallout: New Vegas, and Activision's own military shooter
Call of Duty: Black Ops.