How do I block a reappearing website that I already blocked once?

Its a website that says we need protection bcuz we have 'viruses'. But I already checked to see if I have viruses, and I dont have any at all. The website (about:blank); that website keeps showing up. And I blocked it the best way that I could by going to Tools, Internet Options. And all that. But that website keeps showing up. If any of you guys knows what the problem is..please tell me. -Thanks (: