Complete the indicated task to unlock the corresponding challenge. These challenges will not show in the barracks.

Challenge	Task
...With A Vengeance	Avenge a fallen teammate. 0 experience points.
6fears7	Select killstreak rewards requiring 7, 8, and 9 kills and earn them all. Unknown experience points.
All Rounder	Complete all other challenges. Unknown experience points.
Click, Click, Boom	Kill an enemy with C4 while you are in Last Stand (not Final Stand). 5,000 experience points.
Hard to Kill	Get 2 kills while in Last Stand or Final Stand. 500 experience points.
Hijacker: I, II, III	Steal 10, 50, and 200, enemy crates. 1,000 experience points, 3,000 experience points, 5,000 experience points.
Infected	Get knifed by an enemy wearing this title. 1,000 experience points.
Living Dead	Survive in Final Stand long enough to get back up. 1,000 experience points.
Martyr	Get a kill with Martyrdom grenade. 1,000 experience points.
Martyrdoh!	Kill an enemy who is priming a grenade. 0 experience points.
Never Forget	Get hurt by an enemy, survive and backstab the same enemy. 3,500 experience points.
Ninja	Defuse a bomb right after it is planted while the planter is still alive. 2,000 experience points.
Point Guard	Most assists in a game. Unknown experience points.
Radiation Sickness	Get nuked by the enemy. 1,000 experience points.
Renaissance Man	Get three kills with three different weapons in one life. 1,000 experience points.
STD	Transmission Complete (Knife an enemy wearing this title). 5,000 experience points.
Sidekick	Get three kills with your secondary weapon in one life. 1,000 experience points.
The Avenger	Avenge the death of 3 teammates in one life. Unknown experience points.
The Edge: I, II, III	Get the Game-Winning Killcam 5, 10, and 20 times. 1,000 experience points, 5,000 experience points, 10,000 experience points.
The Loner	Get a 10 killstreak with no killstreak rewards selected. 2,500 experience points.
The Numb	Take enough damage that would normally kill you with Painkill active. 0 experience points.