Turn on [NumLock] then press [Keypad 5] at the main menu to display a password prompt. Enter one of the following case-sensitive passwords then click "Submit" to unlock the corresponding level.
Note: This code only works on v1.2 and lower. Tun on [Caps Lock] then hold [Shift] + Z + Enter at the "Level loaded; press [spacebar] to begin" message to advance to the next level.