During play, hold down 'HELP' and press the left mouse button. A secret screen will appear. While still on the secret screen press the 'LEFT AMIGA' key 5 times and then press 'SPACE' to go back to the game. If you hold 'HELP' and press the left mouse button again, you will notice that the secret screen now shows that the cheat mode is now on. You will now be invincible.