(And it's one of the reasons you might not want to upgrade to Windows 10 just yet.)If you're running a professional version of Windows 10 (Professional, Enterprise or Education), you actually can disable automatic updates using the Group Policy editor.
Update, May 15: With the Windows 10 Creators Update, Microsoft has largely addressed the forced updates that often resulted in lost work.
And, while the the recent Wanna Cry ransomware does not (thus far) appear to affect Windows 10, you need to make sure your PC is kept up-to-date with security patches to avoid exactly those sort of attacks.
The problem I am having is that the options my Automatic Updates window are all grayed out.
It is set to "automatic", and it won't let me change anything.
To that end, consider the information below to be out of date, with a more thorough update to come.
As a general rule, an up-to-date operating system is a secure operating system, and some people are terrible at updating their operating systems.
But if you -- like most people -- are using Windows 10 Home, you'll need to use workarounds to stave off Windows 10's aggressive automatic updates.
The most obvious -- albeit laborious -- solution is to install updates at times when it's convenient for you.
I understand this is controlled somewhere in the policies, but I can't find anything about auto updates in any of the policies screens.
I also can't find anything in the Registry that looks like it controls this.