We get sham calls from India all the time (the code comes up in the caller-ID display) from those call centres, usually trying to sell us something. There seems to be quite a racket of cold-calling people just to gauge the response and work from there. I can always tell it's phony anyway, because they ask by name for the previous owner of this house, who hasn't lived here in years!

- Don't touch it. With a barge pole.

- Don't get into conversations - it encourages them - though you can say you'll report him to the phone company for harrassment if he doesn't leave you alone. (He probably keeps trying because you haven't put the phone down in his ear.)

- See if you can find out the number he's calling from.

How on earth would he know whether you have Malware or not??! If you did want to engage him in any dialogue (which I wouldn't) ask him to confirm back to you what your computer number is. Or tell him you've just dumped it and bought a new one. But really, the less you say the better. And if he keeps hassling you, note down the dates & times and make good on your threat to report him to the phone company.