On Macs running the latest version of High Sierra — 10.13.1 (17B48) — it appears that anyone can log in just by putting “root” in the user name field. This is a huge, huge problem.
To be safe, do not connect your system to the Internet until Apple resolves this problem.
Read details at this link: https://techcrunch.com/2017/11/28/astonishing-os-x-bug-lets-anyone-log-into-a-high-sierra-machine/
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