This isn't a spoof scam or spam - this happened to someone at work yesterday. His wife got a call from a guy claiming to be from Microsoft, he stated that her PC was running slow (which is was). He got her to reveal her IP and tick the allow remote control in advanced system properties. He then grabbed control of her system and started rifling though her pictures and demanding money for security software to fix the slowdown issue.
She shutdown the laptop when they started demanding money. Her laptop had Norton 360 installed but this is no defence if you allow someone to remote to your PC. Companies like Microsoft would never cold call you like this, only when you have raised a ticket with them.
More details here:http://www.computeractive.co.uk/computeractive/news/2267232/police-act-shut-cold-call-scam?page=2
It's seems such a stupidly audacious scam that no-one in there right mind would fall for it, but as with all scams there's always someone who will.