This is a VERY popular scam at the moment. Several threads on it on Gransnet. There must be a grapevine of "latest ways to diddle the public" because it seems to be individuals, not an organisation.
They phone you out of the blue, tell you they are from Microsoft Windows Technical Team, or some such fictitious entity , and that they have reason to believe you have a virus. Then they take you through a lengthy procedure to get rid of it, which involves you doing things in parts of the system you ought to leave well alone. Then they charge you, taking your credit card details.
After that they say you can take out a maintenance contract so that it will never happen again, taking more from your credit card.
Finally they leave you feeling so happy to be safe from those pesky non-existent viruses - until you discover that they are now able to dip into your credit card at will.
MICROSOFT WINDOWS ORGANISATION CANNOT TELL WHETHER OR NOT YOU HAVE A VIRUS AND EVEN IF THEY COULD THEY WOULD NOT OFFER TO FIX IT FOR YOU