Alot of people password protect their macs, and for good reason, however there is a buildin backdoor if you forget your password on a mac and its called Single User Mode. To get to single-user mode, hold down the command/cmd (cloverleaf) and “s” keys as the system begins to boot. This will drop you into a command line interface before the system has fully started up, giving you the chance to check/repair things before the normal OS X GUI environment starts up. What baffels me the most is, that it doesn’t requere a password.
Now your are free make the hack:
mount -uw /
This will make OS X believe, that the next time it boots it’s first boot, and let you create an administrative acount.
To prevent people from using this backdoor enable firmware password on your mac. This i done by booting into recovery mode, pressing CMD+R at startup and when started, click the Utilities menu and select “Frimware Password Utility”. This also prevents thieves from reinstalling your mac, if stolen, because they will have to type the password to boot into either OS X, recovery or Windows for that mather.