Just had some guy on the phone claiming to calling from Microsoft saying I needed to upgrade my OS (at the cost of 150 quid) because my machine was downloading viruses, and this had apparently been picked up at Microsoft HQ. (Yeah, I'm sure they all sit around keeping guard over my computer).
I was rather suspicious because he didn't know the first thing about my machine - OS, browser, ip number etc - yet claimed it was all being tracked.
Anyhoo, when I challenged him about his lack of knowledge he hung up, but I did get the number via 1471. A quick search of Google revealed that this is a known scam, so if you receive a similar call, do not give them any personal information, especially your bank details. IME Microsoft never phone customers, and upgrades are free and automatic via the actual computer that needs the upgrade. You do not need to pay to download anything or have discs sent to you.