Secrets
After beating "Call of Duty 4: Modern Warfare," Arcade mode becomes available for players. Additionally, after beating the game, wait until the credits have finished rolling and a new mission will automatically begin. The mission takes place on a plane and requires that a passenger be saved within two minutes. Both Arcade mode and the secret mission are earned by besting the game on any difficulty level.
Intel
Items called Intel Pieces are hidden throughout the game. Collecting these pieces will give players new cheat options. The more Intel Pieces you collect, the more cheats you will unlock. Collecting two Intel Pieces opens up CoD Noir, a cheat that will let players play in black and white. Finding four Intel Pieces unlocks Photo Negative mode, which allows players to play an environment with inverted colors. The game's contrast will go up if the Super Contrast cheat is unlocked after gaining six Intel Pieces. Eight Intel Pieces will unlock Ragtime Warfare, a cheat that transforms the game into a silent film atmosphere. Cluster Bombs, which create bigger explosions, are earned with 10 Intel Pieces, while it takes 15 pieces to unlock A Bad Year, a cheat that makes enemies explode. Slo-Mo Ability slows the game down 40 percent and is earned with 20 Intel Pieces. If all 30 Intel Pieces are found, Infinite Ammo is earned.
Weapons
Earn special golden weapons by finishing specific challenges. While the weapons are not more deadly, they do look different. If you finish all of the Assault Rifle challenges, you'll earn the Golden AK-47. The Golden Dragonuv is added to a player's arsenal after completing ever Sniper challenge, and the Golden M1014 appears after beating all of the Shotgun challenges. Completion of every LMG challenge earns the Golden M60, while finishing each SMG challenge unlocks the Golden Mini-Uzi. You can only earn the Golden Desert Eagle by reaching level 55 in the game.