World of Warcraft expansion, Cataclysm, has sold 4.7M units since its release. The expansion went on sale worldwide on December 7. In the first 24 hours of release, it had sold 3.3 million units.
Blizzard boss, Mike Morhaime boasted, "We created thousands of new quests, introduced new lands to explore, and extensively revamped the game world for World of Warcraft: Cataclysm, making it our biggest and most ambitious expansion yet. We’ve been floored by the community’s response so far, and we’d like to thank them for their continued passion and support for World of Warcraft, and for helping Cataclysm reach this incredible milestone."
Blizzard is not resting on its laurels, however, as they have already begun planning on a fourth expansion, though this one will be more like The Burning Crusade and Wrath of the Lich King in opening up a new continent or dimensional land.