Backup

I decided I should back up my computer.  So I set it up to run the backup over night and went to bed.  When I woke up and checked the computer, I found that Windows had installed an update overnight and restarted my computer.  So I lost my backup and had to do it again.  I have never seen Windows do an update while the computer was turned on.  Usually, it does its updates when I shutdown and I shutdown every night.  So I thought I was up to date.  What were the chances that they would update my computer on the same night that I was backing up my computer.