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If I create a firmware password on my MacBook, what does that protect me from?

Does it protect from any of these:

  • Reformatting the hard drive.
  • Switching OS to boot from (e.g. if Boot Camp is installed).
  • Restoring the laptop to its original factory settings (i.e. reinstalling OS X).
  • Installing another boot loader such as rEFIt which bypasses the firmware password
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Installing a firmware password will prevent anyone without the password from selecting a different boot disk to start up the computer. It will also disable some startup key sequences, like getting into single-user mode. I don't know how the firmware password interacts with something like rEFIt.

However, if someone can open your computer, they can disable the firmware password by pulling one of the sticks of RAM and/or just access your hard drive directly and do what they want with it.

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All of the above can be performed if the person has physical access to the computer.

See the Apple support page I've linked to below, it explains that resetting the PRAM or Open Firmware will reset the password and allow someone to do any of the things you've listed above.

Apple page on firmware password protection

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