Redirection spam on some websites?

So, this has happened on two sites so far. Explosm, and that cheezburger site. A little box pops up at the center top of the page and says "You may be in with a chance to win an iPhone 5" or something like that. It's from a page called cleanmasterapps. What's going on? I'm on Youtube all the time but it hasn't happened there. So I'm wondering, is it something affecting those sites, my browser (chrome) or do I have something on my computer that triggers it? I don't know how these things work. And if it's to do with me, how would I go about fixing it? I just recently cleaned out my history, cache and cookies and all that.

Very simple answer.
http://my.opera.com/dr-flay/blog/how-to-block-sites
http://my.opera.com/dr-flay/blog/online-anti-malware