Apparently strange usage is showing up on their servers and they think I have a virus or worse. My usual response is “What on my Mac?”
However for the unwary they can be very convincing and they can find some error messages that look a little threatening but is completely normal. After fiddling around on your computer a little they then charge you £300 for the fix.
Of course during this whole event they have often taken access of your computer and have planted some sort of malware on it or a variety of other things none of which are useful to you! To read more see this link, and another link here.
It does not matter how convincing these people sound, no-one is actually going to phone you to tell you your computer has gone wrong unless it is a scam … put the phone down and do not listen to their arguments.