Foreboding Instances

Over the past couple months I keep getting these popups on my computer that are a gay facebook. It was bothering me because I don't go to websites that generate those types of popups. I also noticed that whenever I saw these popups my computer's website history was also deleted. Today I realized there was a connection. My brother had gotten on my computer each time the history had been deleted, and every time that same popup was there. So, with all these instances happening on my computer with the same circumstances superseding each one, it leaves me to conclude that my brother is using my computer to watch gay porn and deletes the history on my computer. He's doing it on my computer so if he slips up he can say that I'm the one watching this porn and he will be free of any consequences. If he's caught he can say that he just got on the computer and it was up on the screen. This may be just an extreme coincidence that could statistically be passed off, but in the real world it doesn't really happen that way, does it?