Originally Posted by Aimee G

That could be several things. If you're only getting it on one site, it's unlikely that there's adware on your 'puter. If it was a blog & that blogger paid for hosting & they didn't pay their bill, the hosting company can & will put an ad in that space until the blogger ponies up the dough to get their URL back. Again, it could be a redirect virus. Or it could be that the website you tried to access belongs to a "hub", & every *so many* (I don't know the ratio) times you access a website on that hub, instead of the website, you get an ad.