Hardline

In the "hardline.cfg" file, enter the following line at the end.
It's case sensitive, so type it exactly as shown:
CHEATING IS SOMETIMES USEFUL BUT FOR HOW LONG ???

Now during the game hit the following keys:

[X] Invincibility
[BACKSPACE] Kill all enemies on screen
[HOME] Gain main weapon ammo
[INSERT] Full health (Information from Cheat Machine)