Download and run Malwarebytes as soon as possible.
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Do this in safe mode and it should find and remove the malware.
This is a very common attack in the last 6 months I've removed it from a bunch of computers. Some of them even mimic your normal antivirus screens so it's very hard to determine if it's is real or not. But if you can't get it to go away that's a pretty good sign that it's not.