Studio head Vince Zampella informed CNET of the milestone. He was was unsure of the exact breakdown per platform, but said that the Xbox 360 version is the top-seller. Back in January, studio owner Activision announced that the game had topped 7 million units worldwide and was the best-selling game of 2007.

Since then, the developer has released a new multiplayer map pack for all versions of the game, which set a new record for paid downloads on the Xbox Live Marketplace with over one million downloads during the first nine days of its availability. The free PC edition of the map pack hit today.

The next Call of Duty title, said to take place in a "new military theater," is slated to arrive on PC, PlayStation 3, PlayStation 2, Xbox 360, and Nintendo DS later this year.

The developer of the next entry is presently unknown, though job listings suggest Call of Duty 3 developer Treyarch may return to the franchise, with speculation that Infinity Ward is already working on Call of Duty 6.