I got a call, BUT did not answer, since I didn't know who it is.

This was the phone number call regarding a Microsoft virus.  I asked the person calling to give me a number I could call back. He gave me another number for the call back  (845) 262 -3348.  When I called, it was answered as Microsoft.
The caller had the Microsoft serial number of my p.c.  I thought it was legit, but still did not sound right.
While he was on the phone, I checked 845 phone number it is an old scam number. Watch out.

My son called the 845 number and the person answering did not answer as being Microsoft.  

>> The caller had the Microsoft serial number of my p.c  <<

No, they did not.
Instead, they gave you the code number of a process that runs on all Windows machines.

Educational post:
You may have been exposed to scam # 3, as described here:
http://phonehelp.2truth.com/facts_rev.html

Remember to return here, to 800notes.com, after you look at any of the information at that site.

Thanks,

At least these guys are persistent.  Just received another call from them, this time the number was 915-282-6641.  But he hung up before I could actually get a full sentence out regarding their scam.  : )