In-game, press Alt+H. A box with the title "Cheaters never prosper" will come up, where you can enter one of the following passwords (note that the game strictly uses the US keyboard layout). Press Enter to apply one.

Effect	Password
Bottom border, with which you can't lose the ball anymore	funyons
Explodes the level and you advance to the next one	inc me
Instant ball-4-split item (up to 256 balls)	sweet
Instant extra life	through holy faith
Instant fire ball item	let me hear you say fired up
Instant magnet paddle item	my velcro shoes
Instant magnetize bar item	no ska no swing
Instant paddle growth item	not a small thing
Instant red-questionmark item	detrimental abundancy
Instant rocket item	sidewinders
Trigger game end sequence when finishing the current level	i never prosper