How to turn OFF Automatic updates

I was shocked to wake up this morning to dozens of email messages saying the sites I control have been automatically updated to 3.8.1!

How do I turn that OFF?

I have many many plugins across those sites that are not always compatible with the latest version of WP.

The auto update might have seemed like a good idea, but I see that it is bound to cause all kinds of issues that will mostly be non-billable for me to to pass along to clients that I talked into using WordPress as their platform.

Please tell me the WordPress developers built in the ability opt out of this very bad idea!