What is the Startup Security Utility?
On an iMac Pro, the Startup Security Utility provides firmware password protection, Secure Boot, and External Boot security features that give you control over how your iMac Pro starts up. On other Mac computers, the utility provides firmware password protection for Mac computers that support use of a firmware password.
The Startup Security Utility provides these features:
Firmware password protection: Use a firmware password to prevent anyone who doesn’t have the password from starting up your Mac from a disk other than your designated startup disk. To learn more, see the Apple Support article How to set a firmware password on your Mac.
Secure Boot (iMac Pro only): Use this feature to make sure that your iMac Pro starts up only from a legitimate, trusted operating system. To learn more or to find out how to select a level of Secure Boot security, see the Apple Support article About Secure Boot.
External Boot (iMac Pro only): Use this feature to control whether your iMac Pro can start up from an external hard drive, thumb drive, or other external media. For more information about selecting a level of External Boot security, see the Apple Support article About Startup Security Utility.
Important: The storage drive of your iMac Pro is encrypted with keys tied to its hardware to provide advanced levels of security. Because the encryption features make it difficult to recover files, it is critical that you set up Time Machine or another backup plan to back up the contents of your computer to an external drive regularly. For more information, see Back up your files with Time Machine and the Apple Support article How to use Time Machine to back up or restore your Mac.