On Mac computers it is possible to prevent booting to alternative media which could get around OS X's security.
Post-2011, the only way to reset the password is to take it to Apple to be serviced–they will check the serial number to make sure has not been reported as stolen.
For pre-2011 machines, use the Decoder:
- Boot up the Mac and log into an account with admin/root privileges
- Open the Terminal app
- Run the command:
sudo nvram security-password
- You should get output like:
- Enter the code as displayed (without 'security-password ') into the Hash input text box below and press the Decode button
Developed using the information at c|net's Use the Calculator to reveal a Mac's firmware password