willie_901
Veteran
My i-mac mysteriously starting downloading the new operating system in the background with no indication it was doing so. Amazing considering I disabled all that stuff ages ago!
I have no idea how Auto Update was turned on. I have used OS X since day one on desktop and laptops and every singe an Apple update had to be initiated manually.
If you visit the "App Store' section in the System Preferences panel you can turn Auto Updates off.