How do I get rid of this annoying page that always pops up my screen?

There is this page called Adult FriendFinder which pops up my screen when am using the compute and sometimes I don’t like using my computer when someone is behind me because they would think that I am a perv and looking at porn or stuff like that.
I don’t know how to get rid of it and I don’t want to tell my parents.
Help?
Has this ever happened to you and what did you do?