Leo says that if Microsoft Security Essentials didn't find it, and Nod32 didn't see it either, chances are there isn't any malware on Matt's computer. He could have a browser hijacking object or a browser helping object.
Since it's doing it across more than one browser, it may be DNS Changer, which has changed Matt's DNS settings and is routing Matt's traffic elsewhere.
It could also be that the router has been modified, not Matt's computer. Matt could reset his router or look in it to see if the settings have been altered. Matt will need settings from his ISP to do that, or change it to 188.8.131.52, which is Google's DNS.
He should also run the Microsoft Malicious Software Removal Tool (MRT). Go to Start >> Run >> Type MRT, and hit enter. Do a thorough scan. Then he may want to get another second opinion by running an online scanner like Eset. He could also try MalwareBytes or Windows Defender. There's a chance it could be a toolbar that's been installed on all of his browser, and sometimes those don't show up as malware. He should uninstall those too.