One of our trade association clients was contacted by a what they suspected was a phone scammer today. Rather than falling victim to the scam, they called Hilltop to verify their suspicions.
Microsoft does not make unsolicited phone calls to charge you for computer security or software fixes.
If you are ever suspicious about a call from a technology vendor, call your Hilltop account manager or the Hilltop 24x7 Helpdesk.
See this page on Microsoft's website for more information: http://www.microsoft.com/security/online-privacy/avoid-phone-scams.aspx