Microsoft Scam -Beware flashing warnings

DH laptop yesterday was hacked by a scammer claiming to be Microsoft. A loud claxon alert was heard on his screen and a flashing message using Microsoft logo. He rang the number given and spoke to very plausible woman who was very knowledgeable about computers who said she would sort out the problem with him. suddenly the last four digits of his debit and credit cards came up on the screen and she asked for a payment of £30 to fix the problem. He agreed and he then received a text from our bank for him to authorise a payment of £301 which went through. Luckily I was at home at the time and got straight onto our bank while he continued to speak to this woman. Our bank told him to close his computer immediately. They then took him through a lengthy fixing and cleaning process freezing our account and cards. New firewalls were added to our laptops and we are all sorted this morning.
I would just say that DH is very computer savvy and he was taken in some of the way with this very clever scam. Please be aware.