My parents think I'm gay

It all started last week when I had some friends over. They decided it would be funny to leave gay porn saved on to my computer. My parents were the first to find it. We had a long, awkward conversation at the dinner table and they didn't believe me when I told them it was my friends who did it. They started to check my computer every once in a while, and they soon started checking my emails. Someone had sent me a fake letter saying something about thanks for subscribing to our fag porn site. My parents had a talk with me about this also. Now they think I am gay and they won't allow me to bring any of my male friends to my house unsupervised. This sucks. What should I do to prove that I'm not gay?

BTW my parents are hardcore catholics. They hate gays.