Microsoft releases “C” and “D” updates to people who click “Check for Updates” in Windows Update. Those people become unwitting beta testers. January 2019’s C update has a rare distinction: Microsoft tested it with Windows Insiders first.

C and D updates are released in the third and fourth week of most months. They include non-security fixes and are only installed for people who click the “Check for Updates” button in Windows Update. These people essentially beta test the updates before the fixes form part of next month’s stable Patch Tuesday updates. Those Patch Tuesday updates are named “B” updates, as Patch Tuesday is in the second week of each month.

These C and D updates have caused problems before. For example, a “D” update recently caused blue screens on Microsoft’s own Surface Book 2 hardware. Only people who clicked the “Check for Updates” button would have installed it and encountered the problem. Microsoft calls these people “seekers” and thinks they’re looking for more updates, but we think most people clicking that button have no clue they’re opting into unstable updates.

There’s finally some good news, though! As Woody Leonhard points out at, this month’s C update—Windows Update KB4476976—has actually gone through thorough testing in the Windows Insider Release Preview ring earlier this month:

It’s finally out. The first Win10 patch (to the best of my knowledge) that’s been thoroughly tested in the Windows Insider Preview Ring — and I’d be willing to bet that it’s pretty stable.

…Raise a glass of cheer. We may be witnessing a fix to Microsoft’s fumbled fixing method.

This is still a C update and it’s still only installed if you click “Check for Updates,” but “seekers” who do click that button will be getting a patch that’s already gone through a round of testing with people who know what they’re getting into. Windows Insiders are, of course, people who’ve chosen to be beta testers.

As Woody points out over at Computerworld, Microsoft first pushed a test version of a cumulative update to the Release Preview ring back in November, 2018. But, this time, Microsoft put two builds through the testing cycle, using Insiders to actually find problems before the stable release.

That’s just a month after the release of the initial release of the disastrous October 2018 Update, which deleted some people’s files. Microsoft was so confident in this big update that the company didn’t even bother putting it through Release Preview testing before unleashing it on those unfortunate “seekers” who clicked “Check for Updates”:

As Microsoft’s Brandon LeBlanc pointed out, Microsoft released the patch to release preview at the same time it released it to “seekers.”

Now, Microsoft has been chastened, and it’s even putting smaller patches through real testing before rolling them out. That’s progress!

We just wish Microsoft would stop its shenanigans with the “Check for Updates” button. That button should never opt users into additional, less-tested patches without warning. But at least those patches are getting more testing first.

RELATED: Don't Click "Check for Updates" Unless You Want Unstable Windows 10 Updates

Image Credit: KC Lemson/Microsoft


Profile Photo for Chris Hoffman Chris Hoffman
Chris Hoffman is Editor-in-Chief of How-To Geek. He's written about technology for over a decade and was a PCWorld columnist for two years. Chris has written for The New York Times and Reader's Digest, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC. Since 2011, Chris has written over 2,000 articles that have been read more than one billion times---and that's just here at How-To Geek.
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