Get Silenced Ballers
Get a Silent Assassin Rank in any mission.
Get Sawed Off Shotgun
Get a Silent Assassin Rank in any 2 missions.
Level cheat
At the main menu, press: R2, L2, Up, Down, square, triangle, circle.
God mode
While playing, press: R2, L2, up, down, X, R2, L2, R1, L1.
All weapons
While playing, press: R2, L2, Up, Down, X, Up, Square, X.
Megaforce mode
R2, L2, Up, Down, X, R2, R2.
Full heal
While playing, press: R2, L2, Up, Down, X, Up, Down.
Bomb mode
While playing, press: R2, L2, Up, Down, X, Up, L1.
Punch mode
While playing, press: R2, L2 Up Down X Up Up.
Gravity
While playing, press: R2, L2, Up, Down, X, L2, L2.
Lethal charge
While playing, press: R2, L2, Up, Down, X, Up, Up.
Nailgun mode
While playing, press: R2, L2, Up, Down, X, L1, L1.
Slow Motion
While playing, press: R2, L2, Up, Down, X, Up, L2.
Invincibility
Press R2, L2, Up, Down, X, R2, L2, R1 and L1 at the main menu to unlock invincibility.
Get the M4
To get the M4 you must complete all the St.Petersburg missions, including and up to "Invitation to a party", and recieve a Silent Assasin rating, each time, at the end.
Quick Pick
On some missions where you have to get passed a door you need your lock pick but it takes hours so start to pick then go to your menu and when you go back its done.