I have just taken a phone call from someone who asked me to confirm I was who I was, gave me the correct Postcode then launched into a warning about a serious virus.
They had not identified themselves which immediately put my early morning antennae on the alert, and then said I was to go and switch on my computer.
I said "No" and put the phone down, went upstairs and switched off my computer.
When I dialled 1471 the number was withheld.
Right decision? I think so.