Mission select
Pause the game, choose the "Options" selection, highlight the "Select mission" option, then hold Left + R1 + L1 + Select + Square + X (simultaneously).

All weapons and infinite ammunition
Pause the game, highlight the "Weapons" option, then hold Right + L2 + R2 + Circle + Square + X (simultaneously).
Note: Only the weapons normally available during the current level will become selectable.

Super ammunition for the Silenced 9mm
Pause the game, highlight the "Silenced 9mm" under the "Weapons" option, then hold Left + L1 + R2 + Select + Square + X (simultaneously). If you entered the code correctly, Gabe will say "Understood".

Expert mode
At the title screen, hold Left + L1 + R2 + Select + Square + Circle + X (simultaneously). If you entered the code correctly, the phrase "Damn it" will be spoken.

Weak enemies
Pause the game, highlight the "Map" option, then hold Right + L2 + R1 + X (simultaneously). If you entered the code correctly, you will hear a laugh.

View FMV sequences
Locate the area in level 1 where your character goes through a window to get to an elevator. Go straight and jump over the boxes. There are pictures on the wall that resemble doors. Approach the middle picture where the Flak Jacket is located. Then, pause the game and enable the "Weak enemies" code. The game will resume in a movie theatre. Walk into the entrances to the theatre (the curtains) to watch the FMV sequences. Press X to advance to the next FMV sequence or press Start to exit.

Hints

• Survive burning After catching on fire, quickly press Start, then press Start again. You will be hurt, but still alive.
• X-ray vision The virus scanner may be used to look through the walls to find enemies.
• Grenade launcher in level 1 Go out the window in the bar into the back alley. Look up to see two fire escapes. Climb onto the dumpster and get onto the fire escape opposite the bar first, then jump up to the pipes and go hand over hand to the other fire escape. Be careful, because two terrorists will run out to shoot half way across the pipe. After taking care of them, drop down onto the fire escape and open the box for the grenade launcher. This makes the grenade thrower in the subway section much easier to handle.
• Getting through the subway Go to the opposite end of the subway after it explodes. Use the flashlight on the left of the tracks to find the C-4. Get the C-4, then go to the right hand side. Look up to see the upper level. Press Triangle to climb onto the red crate. Press Triangle to keep climbing up through the debris until the top is reached. This is the only way to exit the lower level.
• Museum gates Find the card keys to get through the gates in the museum. Check all the guards and people that are killed; they usually carry card keys. For the gate in the Rocket Room, shoot the control panel on the third level that keeps sparking while your character is standing on the elevator to reach to that level. The man with the card key is up there.
• Defeating Rhoemer The only way to defeat Rhoemer (the final boss) is with Gas grenades, which can be found in the upper right room of the last level.

Note: This code also gives enemies infinite armor. So the only way to kill an enemy or to be killed is by a shot in the head or an explosion.