Humans 

Cheat:
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Load the game as usual and don't do anything until the 
highscore screen appears.  Type 'COMMANDER' and then 
press the fire button.  After a few moments press F10.  
If your ship flickers you are now invulnerable, and
have infinite expansions and smart bombs.
                                        
F1-F5 - Other Six Levels of 'expansion' (you can still 
        capture the capsules)
F8    - Advance a level (There are three)
F10   - Turn cheat mode on/off

You cannot get a high score with the cheat mode on.