Setting up firmware password protection in Mac OS X
You can use the Open Firmware Password application to set up low-level password protection with Mac OS X 10.1 and later.
Apple Open Firmware Update 4.1.7 and later provide the groundwork for password protecting computers at a low level (Open Firmware Password Protection). This feature is off by default. Apple provides the Open Firmware Password utility for use only with Mac OS X 10.1 and later.
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