Problem now appears to be solved. Many thanks to chub_tor and fruitbat.
Method used was to enter via F8 into safe mode then download firstly malwarebyte, scan and delete offending files then download and scan using hitmanpro as a second opinion malware solution. Thanks also to malwaretips.
I agree with Jock1e - Money well spent on Emsisoft. onthelimit1 also makes a good point - the two most recent variations of this scam even prevent safe mode. I usually use Malwarebytes on a quick scan first followed by a full scan of Emsisoft.
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