First, the update goes through the Windows Insider program, where millions of willing beta testers install admittedly risky code and provide Microsoft with feedback on bugs. All Insider members know there is a risk that something may go wrong; they install Windows 10 on older, “expendable” machines, not primary systems used for daily or critical work.
Second, the update goes through a “Release Preview” testing process before its final release to the public. Microsoft skipped this step in order to release the October 2018 Fall Update during a scheduled press event!
Third, once an update is declared “ready for release” only users who click “check for updates” will get it immediately. They act as a final line of beta testers, their feedback being used in the fourth and final phase of the update process.
That fourth phase is done in stages, with the update going first to users with the most modern hardware and BIOS systems. Their experiences with the update are shared with Microsoft via Windows 10’s built-in telemetry system. (See What Data Does Windows 10 Collect From You?) This data-sharing is part of the “basic” telemetry that cannot be turned off by users. It is used to make last-second tweaks as previously untested hardware platforms receive the update.
Millions of users have believed the “check for updates” option delivered the production-ready version of Windows just a little bit early. But it turns out that only users who checked for updates experienced massive data loss when their premature editions of Windows 10 were installed. Those who awaited the turn of their particular hardware profile did not experience data loss.
The “check for updates” feature now does two different things, only one of which most users are expecting when they click “check for updates.” Their expectation is that they will get bug fixes, performance enhancements, and other improvements to existing Windows software. They do not expect to get a major new version of their operating system with all-new features, especially one that is not fully tested and certified as safe.
Something like this should never happen. I’ve heard of minor glitches when installing Windows updates — stuff like “My printer doesn’t work,” or “Some of my settings got changed.” The worst I can recall in over 30 years of running Windows is instances where the “Blue Screen of Death” popped up and the updates had to be rolled back by going into Safe Mode. But data loss like this should NEVER happen.
Bottom line here is Do not click “check for updates” in Windows Update until the October Update (version 1809) is fully rolled out and the initial raft of bugs are fixed. No one knows when that will be, as of this writing. No one even knows when the rollout of version 1809 will resume.
Security patches will be installed automatically by Windows Update as they become available. You do not need to check for such updates. Just steer clear of the “check for updates” link.