Here's another idea: as soon as they tell you to look in Event Viewer, suddenly start going "oh no! That's not good! What am I going to do about this? I need to get rid of it now! Can you help me make this go away?" and when they ask you what you are seeing, tell them that you have a massive erection >:-) That's really only if it's a man calling, don't use something like that on the ladies. For the ladies, tell them you need to take a massive shit, and can they stay on the line while you do so. This will obviously work better if you can make convincing noises to that effect.

Conversely, when they first say who they are, tell them that you are kanjoos makhi choos (pronounced CON JUICE MACKY CHUCE) and you refuse to pay even one penny.

And then there's this: http://www.myinsults.com/all-insults/hindi-insults - if they can call you bad names in English, why not return the favor. Bonus points if you pretend to go along with their scam while randomly throwing Hindi insults in every so often. When they ask what you just said, play innocent :-P