I've actually dealt with this same exact infection before, not even half a day ago. I've already removed it, but I'm not allowed to post removal advice... though I will say the thing you're infected with will not affect anything you download, so it isn't that hard to remove. Just persistent.
Edit: just in case other people come here from google since this seems to be a sudden widespread infection (sample size of 2, so I'm not sure this is widespread, but just in case) - if you get "ads by Round World" appearing on a Google Search, or something similar, then you have what this guy is infected with.
To help identify if you're affected, do a generic google search. After you get a page of results, you should see five additional ads pop up along with a light grey bar at the top of the page. A yellow box with ads in it is NOT an infection, though if you see more then three of them on the same page you might have a different infection.
Edited by commandhat, 11 March 2015 - 04:00 PM.