Infinity Ward has revealed that Call of Duty: Modern Warfare has over 13 million players on Xbox Live, which is two million more than in March.
That's more than even World of Warcraft, although Infinity Ward claims no monthly subscription fee from users.
"The Thing we learned the most probably is how much focus goes into multiplayer," Infinity Ward's Robert Bowling told Larry "Major Nelson" Hryb. "I mean Call of Duty 4 on Xbox Live just exploded.
"Right now we're 13 million unique users on [Xbox] 360, and that's insane."
And it's more than triple that of PlayStation Network, according to what Bowling said in March.
Bowling promises gameplay footage at E3 next week, which we'll be at and on-hand to see.
Modern Warfare 2 is due out for PC, PS3 and Xbox 360 on 10th November.