Microsoft Says It's Fixed That Windows 10 October Update Bug That Mass-Deleted Entire Directories

By Tom McKay on at

Over the weekend, Microsoft pulled the latest update build of Windows 10 (version 1809) after a bug that flew past its Feedback Hub without the company’s notice resulted in mass file deletion for some users. Now, the company’s director of program management for Windows servicing and delivery, John Cable, says that the bug has been resolved.

Cable wrote in a blog post that the issue, while serious, affected only a very tiny number of users who installed the update in advance of its wider release (which would have resulted in all Windows 10 users receiving prompts to install the buggy release):

In this case the update was only available to those who manually clicked on “check for updates” in Windows settings. At just two days into the rollout when we paused, the number of customers taking the October 2018 Update was limited. While the reports of actual data loss are few (one one-hundredth of one percent of version 1809 installs), any data loss is serious.

(That still means several hundred people likely lost files, per ZDNet’s estimation.)

According to Cable, the bug was related to how Windows handled a feature called Known Folder Redirection (KFR), in which “known folders of Windows including Desktop, Documents, Pictures, Screenshots, Videos, Camera Roll, etc.” are reassigned to different locations on a machine’s hard drive. After an April 2018 update, some users reported that they had empty, duplicate KFR folders, but the method used by version 1809 to clean up those useless folders could sometimes result in Windows deleting everything in a directory that actually contained files. Here’s one of the examples Cable provided in the blog post:

Using KFR the user redirected a known folder to a different drive. For example, suppose you ran out of space on your C drive. You want to save some files separate from your primary folder, so you add another drive to your system for these. You create “D:documents” and change the location of the files known folder from the original “old” location c:usersusernamedocuments to D:documents. In some cases, if the contents of c:usersusernamedocuments were not moved to D:documents, then a user could also encounter this issue. When the October 2018 Update was installed the original “old” folder was deleted including the files in that folder (in this example c:usersusernamedocuments would be deleted; d:documents, the new location, would be preserved).

Microsoft missed the bug despite users filing reports in its Feedback Hub, since the number of total reports of file deletion was too low to trigger a quicker response by its engineers. According to Cable, the company has activated a feature “for users to also provide an indication of impact and severity when filing User Initiated Feedback” to better ensure that serious issues actually end up in front of an engineer.

“We expect this will allow us to better monitor the most impactful issues even when feedback volume is low,” Cable wrote.

It’s safe to say that this was a close call: Many users already despise forced updates even when they don’t delete entire directories. Cable wrote that the October 2018 update, which includes features like a cloud clipboard and an early version of its phone mirroring software, won’t be released until engineers have verified it will not clear out users’ files for them.

Microsoft said its remote and in-store support staff will attempt to assist users impacted by this bug recover their files, though the chances of finding everything intact are probably not so great. If Windows 10 deleted all your shit and you’re feeling brave, you can always try your luck at recovering the files yourself. [Microsoft via the Verge]

Featured image: Elaine Thompson (AP)