That's nothing to do with "LAN security"..it's just local NTFS permissions. Similar to "taking ownership". This hasn't changed in years, most people that work with computers know this. Say a hard drive went belly up, Windows doesn't boot anymore...you'd want to get your files back right?
This is all done under an account with local Administrator privs. If you don't want that 3rd person using the computer to gain access, don't give them admin privs.
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