Apple may have reacted very quickly to patch a major security vulnerability in macOS version 10.13, but it might have wanted to spend a little more time on the solution. It turns out that the update to 10.13.1 removes the security patch in the event that the Mac was not rebooted before updating.
The vulnerability being patched is a rather severe issue that allows anyone root access to the mac without a password. Apple rushed out a patch to fix the issue within 24 hours; much to the relief of the security community. However, Wired has reported that the patch itself has some issues and the computer must be rebooted for it to become permanent.
Those that who installed the security patch and updated to 10.13.1 without restarting the Mac will have to reinstall the patch. Curiously, Update 10.13.1 was supposed to also contain the root vulnerability patch, but it would appear that there has been some sort of miscommunication within the company.
Still, this is a minor issue. One that is easily resolved by the user with no outside intervention. Apple has also updated its support page to reflect this rather necessary step.