Thanks Molly! you have just reminded me of the excellent Over The Wire free hacking/security games: overthewire.org/wargames/
For something seasonal, and significantly more challenging, the annual SANS Holiday Hack is also very good: holidayhackchallenge.com/2018/
I would highly recommend hackthebox.eu. Lot of free VMs and other stuff suitable for both beginners and advanced infosec-oriented people.
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