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