As promised, Apple has released a Mac security update to patch a major macOS High Sierra issue. Security Update 2017-001 is now available through Updates on the Mac App Store.
At the time, Apple explained:
We are working on a software update to address this issue. In the meantime, setting a root password prevents unauthorized access to your Mac. To enable the Root User and set a password, please follow the instructions here: https://support.apple.com/en-us/HT204012. If a Root User is already enabled, to ensure a blank password is not set, please follow the instructions from the “Change the root password” section.
If your computer has public access, you should download this Mac security update as soon as possible. For more information, visit Apple’s support website.