I had two calls in one week claiming to represent Microsoft. Both callers were from India, the first, I let him go through the process of informing me the computer is infested with lots of nasties and offer to clean up the mess at a price. All he needed was permission to access the computer and my banking details.
How much? Well that would be decided once it was determined how many nasties needed removing. Before I could say, "This a con, I'm calling the police!" For some reason we were cut off.
The second two days later, introducing himself as representing Microsoft, I interrupted and said it was only two days ago his brother phoned me and he had the details. This time I put the phone down.
Microsoft will never call anyone about anything to do with a personal computer. Neither will they email anyone about anything, other than to send out email newsletters consistent with a prior consent.
You might think that it makes common-sense not to allow a random caller to have access to a computer, but not everyone understands the dangers involved, and not everyone understands that Microsoft would never make calls like this.
I had a spate of these calls and reacted in a variety of ways. But still it continued, with up to two calls every week. I finally asked the caller to listen carefully because it was a bad line and used a personal high shrieking alarm. After three more calls using this technique the calls stopped.
I know the phone system limits the loudness of sound that comes out of a phone, and it can't transfer a wide range of sound frequencies either, but it worked anyway.
I always start by insisting them telling me what number they have dialled - I do not tell them what it is as it is usually a computer going through all numbers. Then I ask for a call back number in case I want to follow up the issue: if they won't give one I ask to speak to a supervisor. Then I prevaricate saying the householer is upstairs etc, and if I have the time keep going until they go away having wasted a lot of call time.I never give them any details.