Open Firmware Password protection

A securemac.com article discusses the password protection built into Apple's latest Open Firmware update. "It introduces support for additional security options which allow the Open Firmware to be password protected. Similar to the typical PC BIOS password protection feature, this feature in Apple's implementation of Open Firmware allows you to password protect your computer's ability to boot. Furthermore, Apple went above and beyond the Open Firmware 1275 specification and added a progressive delay technique to discourage brute force hacking of the Open Firmware password."

See also Apple's previous TIL article (106292) on this matter. For your info, here are some details on what Apple does not want you to do:

Go into Open Firmware by holding down Command-Option-O-F at startup. Type "password" and you will be requested to type and confirm a password. However, the password is not actually used until you also enable the "security-mode"< variable (setenv security-mode mode). You can set "full" mode, which prohibits booting until the password is entered. The default mode is "none," which is no security at all.

The risk here is that, with full mode enabled, if you forget your password or the Mac does not accept it for any reason, you are locked out of your Mac. Stephen Jonke also warns that there have been reports of the password getting corrupted if this feature is enabled when you update the firmware.