Just recently started getting these. Tried Malwarebytes and a Combofix scan and it didn't clean it. Also ran an AVG Free scan and nothing came up. Happens on both Chrome and Firefox. On Chrome you can click the X and it goes away, but you can't on Firefox.
I think it reset some either proxies or DNS redirects, and I didn't notice anything in the hosts file but I notice my google searches on Chrome are getting redirected and were also on Firefox until I disabled the proxy settings in there, so it had to mess with some proxy settings at least.
I also noticed at the top of Google search results there's entries for traffic.*******.com, so I think that has something to do with it. I'm leary to click on anything because of being hijacked.
Speaking of hijacked, I ran a Hijackthis scan and there were too many things in there I was unsure of so I haven't gone that route yet.