Have you seen this before?

Well no i haven't had any experience with this kinda thing because i'm only 15... But if i were you i would check his computer when he's not home. But if I were you and walked in on him and he was blocking the screen i would be like " Your in my house using my power blah blah blahhh i have the right to know what your doing." Or something along those line. Sorry if im not any help.