Cheat PC Games

Cheat Codes:
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Press [F9] + [F10] during game play to enable cheat mode. Then, press
one of the following codes.

Result Code
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Give 250000 points - F3
Extra life - F5
Extra missile - F6
Extra firepower - F7
Next wave - F8

You have to go to the option tab and then to gameplay. Check the cheats
on tab. Return to the main menu and start the game, what ever strength
you like.

Cheat:
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first go to the play area(solar system) when a chicken comes ram it with
ur plane! (this is not a joke!)Do this until all your lives are gone.
Then go to the play area (solar system)again and you will see that you
are having 16 lives , 16 missiles and all unlockables will be unlocked!

See Also GTA IV Cheats Codes and Deus Ex Cheats Codes Enjoy :)