Some foreign sounding person who told me that he was from Windows Technical Department and that they were detecting unusual operation of my computer from a virus or malware. They wanted me to start up my computer to check on this. It was obviously a scam to get me to allow them full access to my computer. If I had more time I would have played along with them longer to see what commands they wanted me to enter.
I checked my caller ID and they've called three times in the past two days.