Last Friday, Microsoft pushed a patch down the Automatic Update chute. Like so many patches before it, KB 4033637 was completely undocumented. Those running Win10 1607 who hadn’t taken steps to block forced patches found they had a newly revised program running on their systems — and nobody had any idea what the patch actually did.

Informed conjecture said it was an update to the Compatibility Appraiser, to help Microsoft upgrade machines to newer versions of Windows. Other guesses were all over the map. On Reddit, a poster relates how he called Microsoft and was told that it’s a hush-hush security patch for Flash. Microsoft’s own Answers Forum is littered with posts blaming KB 4033637 for system freezes, second screen problems, installation hangs and more.

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