These tend to be bogus as Microsoft will not phone you up stating that they have scanned your PC and found malware or issues that you need fixing.
“Cybercriminals have been calling people on the telephone, claiming to be from Windows or from Microsoft, and offering to help solve their computer problems. Once cybercriminals have gained your trust, they can:
- Trick you into installing malicious software on your computer.
- Take control of your computer remotely and adjust settings in order to leave the computer vulnerable.
- Request credit card information so that they can bill you for the phony services”
Read more HERE from the MSDN Security Tips Team