1. Download this mpdata file.
mpdata.txt

2. Go to Start -> Run-> Type regedit -> Hit Enter.

3. Go to HKEY_LOCAL_MACHINE -> Software -> Activision -> Call of Duty 4

4. Double-click codkey

5. Save the key in notepad

6. Replace the key with: DL2J8PY44Q22GE4888D2

7. Press OK and close regedit.

8. Navigate to your Call of Duty 4 profile folder (typically “C:\Program Files\Activision\Call of Duty 4 - Modern Warfare\players\profiles\your_user_name”)

9. Back-up and then remove all the files in your user name folder.

10. Place the mpdata file you downloaded in your user name folder

11. Open the COD4 MP game and check your rank. You should now be level 55 with all challenges, guns, and every camouflage unlocked!

12. Finally, in the game go to Options -> Multiplayer Options -> Key Code and type your original cd key you have saved in notepad.