Don't leave your Mac unattended before installing the soon-to-come security patch!
There is a security flaw in the latest version of mac OS (High Sierra 10.13.1 - 17B48) that allows anyone to gain access. All they have to do is go to Preferences --> Users & Groups --> click the lock icon and enter "root" for the User Name and no password. VOILA... they can now create new admin accounts.
https://techcrunch.com/2017/11/28/astonishing-os-x-bug-lets-anyone-log-into-a-high-sierra-machine/