I foolishly answered one of those telephone "surveys" recently. I was quite alert to identity theft possibilities, I hope, and didn't tell them anything they didn't already know about me. To every question that started "would you consider changing..." or "are you interested..." I said a firm "no". Then I got this call from the electricity co - pretty sure it was EON - and told them I was with the TPS, so she said "I'm calling because you answered a survey" and it was in the middle of my pointing out that I had said I was not going to change my supplier that she put the phone down. Note to self, stick to guns with all cold callers and do not attempt to be selective.
Did have one of those fake-virus calls once. DS2 answered it and wasn't nearly suspicious enough, so I took charge and ran rings round them for the next 20 minutes. (Anyone for example who claims to be working on behalf of "the Windows company" might reasonably be expected to know the Windows Company's real name, don't you think?) The same guy called a couple of days later and started on the same script, so I greeted him warmly and reminded him of our previous discussion. Never heard a phone go down so quickly.
Found out later that XH wasn't so bright and got scammed out of 50 quid by the same people. Amused me rather because he always used to say I'm too gullible (which is true, see first paragraph above) and never, never to tell anybody anything over the phone (even if it's my bank who I called first). But if it's got IT in it his eyes glaze over.
Oh, another favourite recently is the payment protection insurance one. They are working on behalf of the government (won't say which Department/Agency) to help people recover overpayment of mis-sold insurance. The one I had this week put the phone down when I asked "for what?" It's quite insulting when they don't even try to be convincing.