Moved this to a more appropriate spot for better attention. No antivirus, no matter what brand, is good at detecting or removing these things.
The first thing to do when one of these becomes evident is DON"T CLICK ANYTHING AT ALL, NOT EVEN THE 'X' TO DISMISS IT - however in this case it's obviously too late, then you would power off and then back on into Safe Mode and use System Restore to take you back to before it started. If System Restore is still possible try it..
If that's not possible, try donwloading and running Stinger and Malwarebytes Free, both from the last link in my signature below, and in the case of MBAM, do NOT accept the trial, or you will get the wrong version.