My account was hacked.

I got a message from microsoft that my account had been hacked. I did the necessary steps to reset password. Ran virus detection, malware detection and transfered some accounts to another email account but now I am worried and need to know. Number 1, who hacked my account. Number 2, how long was it in jeopardy before I was notified. I am worried now I am being set up for identity theft. Anyone know how to determine any of this? Thanks