The following procedure involves editing a game file so it is advised that you create a backup copy of the file before proceeding. Using a text editor edit the 'config.cfg' file in the 'Players' directory in the game folder adding the following line to the end of the file:
Seta thereisacow '1337'
Modify the file by binding any of the following cheat codes to an unused key. For example, adding the following line will bind the God mode cheat to the 'O' key:
Bind o 'god'
Save the 'config.cfg' file and then Right click it. Select 'Properties' and set it to 'Read Only'. Begin gameplay and start a new level either by starting a new game or using the 'Mission Selection' option. Then during gameplay tap the binding keys to activate the corresponding effect. There is no confirmation that a cheat code has been activated.
When you have completed Campaign mode this bonus level which is entitled 'An Evening with Infinity Ward' becomes available and contains ALL weapons and vehicles featured in the game, the vehicles though are not to scale and cannot be driven.
This dangerous technique which is known as 'cooking' and prevents enemies from having enough time to throw your grenades back at you is done by holding your grenades for two seconds before throwing them.