Soon after Microsoft made the Windows 10 October 2018 update available for download a few days ago, users quickly discovered an annoying bug: the upgrade ended up deleting user data on some systems. Microsoft halted the rollout of version 1809 to investigate the matter, and found a fix. That means you’ll be able to upgrade to Windows 10 October 2018 update without fearing loss of data.

Microsoft said in a new blog post on the matter that the software upgrade was available initially only to those people who requested it, by checking for updates. The company says the number of customers who got build 1809 was limited. Nevertheless, the data loss was serious for those affected:

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.

Microsoft says that the new Windows 10 release is available to Windows Insiders for the time being, with a broad rollout to follow, assuming there won’t be any issues with the new version.

The company determined that the data deletion issue resides with a bug related to the Known Folder Redirection (KFR) feature. If KFR had been previously enabled, intentionally or by mistake/automatically, but the files remained in the old location instead of being moved to the redirected location, they ended up being deleted. That’s because Microsoft attempted to fix a previous KFR issue from the April 2018 upgrade, where KFR would create duplicate but empty Known Folders.

Microsoft explains it has identified and fixed various scenarios in which KFR files were deleted, so you should no longer encounter the issue. The company will be helping users who have lost data after upgrading to the October 2018 release, although it can’t guarantee the recovery of lost data — check this page for more details about obtaining assistance.

If you’re a Windows Insider, you can upgrade to version 1809 right now. Everyone else will need to wait a while longer. While you wait, you should consider backing up your data.

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