I was recently infected by Windows 7 Internet Security 2012 and with the help of bleepingcomputer.com I was able to get rid of it. I had Malwarebytes installed, which didn't find the malware after 2 scans, but RKill found it when it terminated it, and, using the Shredder that was installed on my computer, I removed it from my computer(bad idea to use Shredder to remove files? not sure).
With that said and done, this virus left some damage behind with it. I cannot start up Windows Defender or Windows Firewall, and when I checked the dependencies for both, I got the message in the title in the properties window for the driver. Exact message was "This device is not present, is not working properly, or does not have all its drivers installed. (Code 24)." The error codes I get when trying to start Windows Firewall/Defender are : under Services I get : "Error 126: The specified module could not be found." for Defender and "Error 1068: The dependency service or group failed to start" for Firewall. On the Control Panel trying to turn Windows Firewall on gets me : "Windows Firewall can't change some of your settings. Error Code 0x8007042c
Along with this, Microsoft Security Essentials was uninstalled. I re-installed MSE just fine and updated it. As soon as the update was finished it removed a Trojan.
Another problem I'm having(not sure if directly related to Defender/Firewall not working) is that sometime my computer cannot access the internet. However, my computer can communicate over Steam, Skype, Ventrillo, etc., but can not connect to game servers or web pages that weren't saved for offline use. When this happened the past few times, I checked another computer in my house and that computer was able to access the internet just fine.
If any of this helps : I am using a Acer Aspire 5736Z running Windows 7 Home Premium x64. The only virus protection I have is McAfee, which expired already, and Microsoft Security Essentials(which, as explained earlier, had to be reinstalled).
EDIT : Should this have been posted in System Security?