Details
One of the most important security tools for data protection on MacOS is FileVault. With encryption in place it makes it difficult for an outside party to access your data if they get physical possession of the computer. One very large weakness in data protection with FileVault is the level of protection on backup volumes. If the internal drive is encrypted but the external backup volume that goes home in the same laptop bag is not it is self-defeating.
Apple tries to make this mistake easily avoided by providing a checkbox to enable encryption when setting-up a time machine backup. Using this option does require some password management, particularly if a large drive is used with multiple computers. A unique complex password to unlock the drive can be stored in keychains on multiple
systems for ease of use.
While some portable drives may contain non-sensitive data and encryption may make interoperability with other systems difficult backup volumes should be protected just like boot volumes.
Solution
Ensure that backup volumes are encrypted using the Time Machine control or using Disk Utility.
Supportive Information
The following resource is also helpful.
This security hardening control applies to the following category of controls within NIST 800-53: System and Communications Protection.This control applies to the following type of system Unix.