Microsoft deletes deleterious file deletion bug from Windows 10 October 2018 Update

The world now knows why last week’s Microsoft Windows 10 upgrade deleted unlucky users’ files: the software treated the default user directory as ripe for destruction, because it thought the files were elsewhere. The upgrade has since been pulled.

Last week, some unfortunate punters who hit the “download” button on the Windows 10 October 2018 Update received the gift of extra disk space, because they lost their \Documents directories.

On a support page issued on Tuesday, Microsoft’s sparse explanation of the bug is as follows: “An incorrect timing calculation may prematurely delete user profiles on devices subject to the ‘Delete user profiles older than a specified number of day’ group policy.”

Microsoft’s John Cable went into more detail over here.

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Microsoft yanks the document-destroying Windows 10 October 2018 Update

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The bug, Cable wrote, affected people who had used a feature called Known Folder Redirection, a tool for folks who have filled their hard drive and wanted new files destined for their Desktop, Documents, Pictures, Videos, Camera Roll, and other such default directories to be stored on another device, such as in D:\user. You keep can saving files into the usual Downloads folder, for instance, and it’s actually saved on another drive with free space, in other words.

In April, Windows Insider guinea pigs reported a bug in this folder redirection feature that created empty copies of the so-called known folders – the standard issue directories like Desktop, Downloads, etc. To fix that, “we introduced code in the October 2018 Update to remove these empty, duplicate known folders. That change, combined with another change to the update construction sequence, resulted in the deletion of the original ‘old’ folder locations and their content, leaving only the new ‘active’ folder intact.”

In short, the OS would potentially wipe your original known folders if you had redirected them to another drive. The three setups that would trigger the deletion are:

  • A user redirected KFR to a different drive, but only put new files there, leaving their old files in the default \user\ directory. Files in the “old” folder were deleted;
  • The user created a redirection from one folder to another, but again, used that location only for new files, leaving the old files in the default (Cable noted that during KFR setup, users are prompted to decide whether or not to move the files); or
  • Users of older OneDrive clients, who had enabled auto-save. Again, this is because there’s a redirection, but old files remain in their default location, because OneDrive only used the redirect for autosave (for example, in a c:\users\username\onedrive\pictures folder).

There’s still a mystery about why Microsoft let Windows 10 October update ship with the bug, because it was reported by testers of Insider releases in June and August.

Here’s the June complaint: “Yesterday morning my dev laptop upgraded to insider preview build 17692. When I logged in, I was surprised to see that C:\Users\me\Documents<\code> contained only "desktop.ini'.”

Sound familiar? It certainly did to the 57 other Insiders who clicked: “I have the same question.”

And in August, another user upgraded to “Evaluation Copy Build 17713.rs5_release. 180706-1551” and also lost files – and 167 other users made the same report.

The file-trashing update was axed, and a fixed release is now available to Windows Insiders to try out. This comes amid the release of a suite of Windows security patches worthy of any Patch Tuesday, covering “Windows Kernel, Microsoft Graphics Component, Microsoft Scripting Engine, Internet Explorer, Windows Storage and Filesystems, Windows Linux, Windows Wireless Networking, Windows MSXML, the Microsoft JET Database Engine, Windows Peripherals, Microsoft Edge, Windows Media Player, and Internet Explorer.”

Basically, update your Windows 10 machines, and deploy widely when ready and tested. ®

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