I have noticed that people are now referring to Call of Duty: Modern Warfare 2 as Call of Duty 6.  It is not Call of Duty 6.  There are more than 6 Call of Duty games.  It is also not called Call of Duty 4: Modern Warfare 2.  The only correct titles are Call of Duty: Modern Warfare 2, or just Modern Warfare 2.  Also, Call of Duty: World at War is not Call of Duty 5.  Nowhere on the box or in the game does it say Call of Duty 5.  This is like referring to Halo Wars as Halo 4, or Halo ODST as Halo 5.