Was it open-search.com by any chance?
In 8 years of using Macs exclusively I've never had a virus or adware on my own Macs... but recently after finally convincing my significant other to purchase a Macbook Air, she loves it of course but after owning it for 3 weeks, I took one look and oh dear lord! The popups!!!
Basically she went to a dodgy movie website that one of her friends told her about, download a movie which was actually a .dmg file with an 'so called' movie player inside it, which she unfortunately ran!
Unfortunately something which to me is plainly obvious fakery, she wasn't to know... being a new user as far as she was concerned that was perfectly legit... and me thinking I was doing her a favour had turned off the 'Allow only apps from Mac App store and identified developers' in Security and Privacy...
Anyway, long story short all her browsers were re-directed to open-search.com and was generating fake ads all over the place. After an hour of trying to work out where this code was being executed from I ended up downloading Avast! which detected all of it and cleaned up 7 infections.
Scary situation though, been a Mac user a very long time, my GF has a Macbook for 3 weeks and



..so I've installed Avast! on my own MacBook now just incase these guys manage to get a bit more sophisticated... and lets be fair I torrent like a mofo!