Don't know how many are aware of this, but you can accidently start a Win 10 upgrade.
Microsoft sent a Win 10 upgrade into the Windows update section, under optional updates, with it
check marked to install.
If you go ahead and tell your computer to install "important updates" from the important updates section,
it will also start to install Win 10 from the optional updates section.
Lots of folks don't look at the "optional updates" section when they install "important updates" from
the "important updates" section, those optional updates should always be sent unchecked.
Microsoft said it was a mistake that they sent it to users with it check marked "to install".
They said they would correct it.
When I looked at the the optional update section on my computer and my wife's computer it was
still checked to install.
I unchecked both because I'm 90% sure, at this time, I will not be upgrading either machine to Win 10.
Figured folks would want to know about this "little accidental glitch" by Microsoft.