Microsoft claims to have taken care of the inadvertent file deletion issue affecting users upgrading Windows 10, and is rolling out a fixed version to early adopters in its Windows Insider program for further testing.
A few days ago, Microsoft was force to pause the rollout of Windows 10 version 1809, as upgraders complained that files in their computers' Documents, Pictures and Downloads folders had vanished.
The file deletion issue also saw Microsoft pull Windows Server 2019 downloads.
"We have fully investigated all reports of data loss, identified and fixed all known issues in the update, and conducted internal validation," Microsoft's director of program management for Windows servicing and delivery John Cable said.
Cable said Microsoft found that the file deletion happened if users had enabled redirection of Windows user data folders - including Desktop, Documents, Pictures, Screenshots, Videos, Camera roll and more - away from their default location under C:\Users\$UserName.
Some users told Microsoft that the previous April 2018 major Windows Update created duplicate empty copies of these folders if redirection was enabled.
Microsoft decided to remove these duplicate folders through code incorporated into version 1809.
Unfortunately for some users, "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," Cable said.
Cable also identified another file deletion scenario involving redirection of Known Folders to OneDrive storage whereby contents of the original default directory were erased if they weren't moved.
Furthermore, an early buggy version of the OneDrive client with autosave turned on didn't move files in users Documents and Pictures folders from the old location to the new one.
When users upgraded to Windows 10 1809, the software update dutifully deleted the folders in the original location, including the files they contained, Cable said. Microsoft has issued an updated OneDrive client that moves the files as expected.
Cable claimed that very few users were affected by the file deletion problem, but conceded that "any data loss is serious".
Users who lost data during the upgrade to version 1809 are advised to call 13 20 58 in Australia for free assistance with recovering their files, Microsoft said.
Additions to version 1809
Quietly, Microsoft took the opportunity to fix a bug that saw user profiles being deleted due to an incorrect timing calculation.
The new version also received patches for a range of critical remote code execution vulnerabilities, as part of Microsoft's regular monthly Patch Wednesday security updates.
This includes fixes for system components such as the Windows kernel, graphics and file systems, the wireless networking and peripherals subsystems, along with the JET database engine, Windows Media Player and the Edge and Internet Explorer web browsers among others.
One privilege escalation zero-day, CVE-2018-8453, affects the Windows kernel and is known to have been exploited by nation-state advanced persistent threat groups.
Windows 10 1809 won't be broadly released until early adopters in the Windows Insider program have tested the revised update and provided feedback to Microsoft.