Angels have the Phone Box
Hi gypsycomp and welcome to Tenforums.
This is indeed strange. You are absolutely sure you didn't log into the Admin account to install a program, make some changes to the system, etc.? I don't understand how someone could manipulate the computer, if you put it in hibernation when you left. Did you notice if it was installing any updates? I am just wondering if this Windows Update setting has anything to do with it:
Automatically finish setting up PC after update
- Some updates require you to restart your PC and sign in to Windows in order to finish installing the update, which means you might sign in to Windows and find you can’t use your PC until the update is finished. Windows 10 helps prevent this from happening by allowing Windows to use your sign in info to create a special token. This token is used to automatically sign in after a restart, finish setting up your PC, and then lock your PC to help keep your account and personal info safe.