What is the largest selling video game of all time

The Call of Duty Series (PC, PS3, XBOX 360, NINTENDO WII)
Call of Duty
Call of Duty 2
Call of Duty 3
Call of Duty 4: Modern Warfare
Call of Duty: World at War
Call of Duty: Modern Warfare 2
Call of Duty: Black Ops
Call of duty: Modern Warfare 3 (not released until November 9th 2011)