The Default Weapon is a secret weapon and base for all weapons, which appears in every Call of Duty game based on Infinity Ward's Quake 3 engine branch. It can only be obtained via console commands or save-game hacking.
In Call of Duty 2, the left hand is replaced by a strange gray mosaic-like horse and when viewed from third person, it shows a horse with no back end being attached to the player. It resembles odd "finger pistols" with a pink cowbell with text "OWN3D" in Call of Duty: World at War or a small blue box in Call of Duty 4 around the left hand's wrist. The fingers are bent in a strange way.
The weapons have no iron sights, instead zooming the player's view and making the cross-hairs disappear. Using a knife melee attack shows the hands twitch slightly as a knife appears through the back of the left hand. Both hands momentarily disappear from the screen. However, the knife does still work.
The weapon has infinite ammo, low power, and is semi-automatic, but fully-automatic in Call of Duty 4 and Modern Warfare 2. The weapon was most likely created for testing purposes and not deleted. It is also possible that it was created for NPCs with no weapon, for example Sgt. Reznov in "Vendetta". In Call of Duty 4, it can kill an enemy with two shots on Veteran difficulty and has a ten round magazine but only reloads five rounds at a time, meaning that the player needs to reload twice, like the Lee-Enfield which is reloaded using two five-round strips. It ejects rifle shells.
The pickup icon is that of a squished AK-47 in Call of Duty 4, but is a stretched AK-47 in Call of Duty: Black Ops. In Call of Duty: Black Ops, nothing is attached to the arm, but the arm itself is twisted.
If the Default Weapon is seen in online Multiplayer, the person using it should be immediately reported for hacking or using a J-Tag device. Since this weapon can only be achieved through console commands. Which is only acessable on the PC, or hacking.
In Call of Duty: Modern Warfare 3, when looking at a player with the default weapon, it appears to be two gray cones pointing away from the player. The killfeed for it is a squished AK-47.