On the security code entry screen, enter the code "8859" and press 'Return' then enter code "1506" and again press 'Return' (another variation says: enter the code as "1506". It will say you are wrong, so enter the code "8859"). Now enter the correct entry code and then when playing the game pressing the 'Help' key will give you infinite energy (i.e. 'Help' now toggles invincibility on and off. If you lose a turtle, press 'Help' to restore each turtle to full strength, even the dead ones.