These cheats can be purchased from the "Unlockables" menu with Intel Ponts. Activation: Pause during gameplay, and go to the options screen. There should be an option that says "Enter Cheat Code". Enter the given code here. If done correctly, the code will automatically be cleared, and the name of the activated cheat will appear on the list to the left.

Effect - Code

Unlimited ammo - Up, Down, Up, Down, Left, Right
Increased force - Right, Right, Right, Down, Down, Down
Fast movement - Left, Left, Left, Right, Right, Right
Ghost mode - Up, Up, Left, Right, Down, Down
Invisible - Down, Down, Down, Up, Up, Up
One shot kills - Up, Up, Up, Left, Left, Left
Unlimited items - Left, Right, Left, Right, Up, Down

Note: Repeat a code to disable it's effect.