SPAM pretending to be MICROSOFT and your computer has been hacked and they can see it's active now.
(a) the computer hasn't been switched on for 2+ weeks so active now is pretty special !!,
(b) they won't give out the address of their Manchester (0161) office and purport that London is in Berkshire !!
(c) they quickly hang up when ask them for their IP address so YOU can help them with Remote Assistance logon.