On the title screen, type one of the following and then press ‘RETURN’ for even more *extreme* fun in one or two-player mode:
“DUNE”_________For magic laser (penetrates walls), speedy boots and keeping weapons when you die; press ‘HELP’ for funny map
“TERMINATOR”_____________________________For ECM for both players
“LAWNMOWER”____________________For bouncy bullets (rebound off walls) [no bounces limit], speedy boots and keeping weapons when you die; press ‘HELP’ for funny map
A voice will say "Bingo!" if you have entered the cheat correctly. Don’t forget to press ‘RETURN’ after you enter any of the above.
These cheats should work on all versions of the game released too. Again, type one of the following on the title screen and then press ‘RETURN’:
“GIGER”_________For speedy boots and fast seeking lasers (no range limit)
“DALI”___________________________For speedy boots and fast turning lasers (no turns limit)
“ESCHER”__________________For speedy boots and two choice power-ups on every level
Finally, if you think the one player version (contained in the registered version only) is too easy, try typing "HARD" or "INSANE" on the title screen.
[Source: Simon Green (coder), as supplied in the game docs of EXTREME VIOLENCE V7.23 (full shareware release)]