Something installed "Win 7 Security 2012" on my PC yesterday and completely disabled McAfee and took control of the PC. This happened, simply, because I allowed a Web page to load in IE8. I'm using a free trial version of "Internet Security" (McAfee doesn't make it easy to see what version it is) with Stealth Mode firewall and outgoing access only for browsers. This software is nothing more than a "feel good" interface, in my opinion. I won't be buying it - and I'll share my experiences with others.
My sympathies but you wont find an antivirus that will block those kind of fake-alert infections because of the way they work. Hence the need for specialist tools.
There is an excellent removal guide here: http://www.bleepingcomputer.com/virus-removal/remove-win-7-security-2012
Scroll down that page as the first links you will see are adverts.
You could also try McAfee Stinger which is designed to detect and eliminate this sort of thing and is updated daily so always install a fresh copy.
That and other useful tools are listed here: https://community.mcafee.com/docs/DOC-2168