Entry location: campaing and multiplayer
before I tell you any of these cheats you should know that for each cheat you complete you should hear a release of air kind of like a cryotube opening and. you need to be really really really fast at these cheats or they wont work. now its really hard to do these cheats... why? because Microsoft really doesn't want anyone to figure out these hidden cheats. the first cheat is
Unlock all Armor (Spartan)
On he main menu push A,B,Y,A,Y,B,B,X, spin the right joystick clockwise once, now on the d-pad push DOWN, UP, A.
Unlock all Campaign Levels
On the first playable level in the campaign when the video stars hold LEFT on the left joystick. Then when you are walking against a wall or whatever is blocking you (just make sure you hold left and are not moving) push Y,X,A,X,B, LEFT (D-pad) DOWN, UP, LEFT, LEFT TRIGGER, RIGHT TRIGGER A,B,B.
Unlock 999,999,999 Credits
You will have to be on the last level of the campaign.
Once there, hold LEFT TRIGGER and RIGHT BUMPER. Then continue to type in this code.............
On the D-pad,UP, DOWN, LEFT, LEFT, UP, DOWN, LEFT, DOWN, UP, DOWN, A,A,Y,X, X,X,Y,X.
Unlock all Elite Armor
On the main menu press these buttons......
CLICK IN THE LEFT JOYSTICK TWICE, THEN CLICK THE RIGHT JOYSTICK COUNTER CLOCKWISE ON THE RIGHT, THEN PRESS RIGHT A,X,Y, DOWN, LEFT, Y,X,Y, RIGHT, DOWN, UP.
In game (not matchmaking) type in the following code.......
(D-pad) UP, LEFT, LEFT, RIGHT, DOWN, RIGHT, LEFT, DOWN, Y,X,A,X,A, DOWN, UP, RIGHT, RIGHT, DOWN, UP, Y,X, RIGHT BUMPER, LEFT TRIGGER, START.