This certainly is malware of some kind.
Remove any browser add-ons, particularly toolbars. In IE, choose Tools, Manage add-ons. In Firefox, it Tools, Add-ons.
Try a more complete scan with Malwarebytes, Kaspersky Virus Removal Tool or other free anti-malware tool. You may need to make a boot disk on a clean PC and boot from that disk to eradicate some malware.
Consider running a different AV suite than what you are currently using, and enable protection of browsers, e.g. in Avast! select Scan, Scan for browser objects.
The biggest risk is that this malware is intercepting everything you do on the web in order to generate targeted ads.