Well, when you view a page, everything on that page is automatically downloaded to your computer. So I would get one of those HD scrubbers like Eraser to get rid of that stuff. You more than likeley got a Trojan or some kind of malware from visiting random porn sites. You can report those sites if you'd like, but I'm assuming you didn't take the time to see what they were called and just tryed to X out of them ASAP. I'd assume this has happened to people before, and since you wern't searching for it or paid for anything I wouldnt worry too much about it.