EFI firmware protection locks down newer Macs
With Apple's firmware password feature on Mac systems you can lock down the options to select an alternative startup disk, boot to Safe or Single User modes, reset the PRAM, and otherwise start the system in ways that can bypass the security features of OS X.
However, as a security measure the firmware password has been met with some criticism because it could easily be bypassed by someone who has physical access to the system. In earlier Intel-based Macs the firmware password was stored in the PRAM of the system, and was simply read by the system's EFI … Read more