Boot Check is a simple security system designed to keep irritating visitors off of your hard disk. This is done by performing a security check when starting the system.
While it can be easily circumvented by booting from floppy, most irritating users don't tend to be technically capable of realising this fact.
And if, by chance, said irritating users happen to discover your keyboard code, it can be easily and quickly changed.
THE FACTS
To configure Boot Check, simply Command-Option-Double Click it. You will then be prompted to provide the keyboard code. Up to two alphabet/number/symbol keys may be chosen, as well as any of the modifier keys (command, option, shift, caps lock, control).
To activate Boot Check, simply drop it into your System Folder. When the hard disk is next booted (startup up), you must hold down the keyboard code entered above. The keys are checked shortly after the "Welcome to Macintosh" message appears.
If the correct sequence if provided, the Boot Check icon will appear at the bottom of the screen, and you may release the keys. If an incorrect sequence is entered, the "Power Off" message will appear, and the startup process will cease.