A customer of mine just rang me to advise me that a member of their staff at a remote branch office had received a call claiming to come from Microsoft saying that their machine had been sending out spam or similar and that they could connect remotely and deal with the problem.
They declined saying that they could not do it right now, but could tomorrow and the call ended.
Microsoft are not in the business of phoning their customers to resolve their problems over the phone, so the calls were clearly bogus.
The calls were apparently very convincing and I am sure that there will be lots of people that will fall for the scam and no doubt end up with bigger problems on their hands.
If you receive such a call, please decline any offers of remote support and hang up.