Sandbox update causing issues - assume production will not be automagically updated?

Our full sandbox got automatically updated to 7.20 overnight and it broke more than we expected to have break. What is the process for making sure that no more sandboxes get updated? And - most importantly - making sure that production does not get automagically updated? Thanks!

We have identified what happened here (And shot the responsible parties).  Rest assured your Production instance will not be impacted and we are working to identifiy what is happening with your sandbox.  We’ll take care of you.