system
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I wouldn't share a PC with this friend unless he conformed with my rules for users.
They are a couple. She is more technologically knowledgeable than her boyfriend who doesn't want to use any common sense security program. So, he, did a clean install over her programs and files.
I guess your friend bought this PC - if so there is even more of a case to say my system my rules if you don't like it get your own PC.
Not everyone can afford a PC of their own.