Microsoft has alerted customers to a critical issue where the File History backup utility becomes inoperable following installation of September 2026 security updates on certain Windows systems.
File History, a legacy backup mechanism that debuted with Windows 8 before being superseded by Windows Backup (which syncs to OneDrive), provides automated snapshots of user files. This allows recovery of accidentally removed or corrupted documents from previous points in time spanning hours, days, or weeks. The feature typically stores backups on external media such as USB drives or network-attached storage, covering standard user directories including Documents, Music, Pictures, Videos, and Desktop folders.
According to a service notice reviewed by BleepingComputer and initially identified by Microsoft MVP Susan Bradley, the company stated: "After installing the September 2026 Windows security update (the Originating KBs listed above), some customers using File History, might be unable to create or update backups. File History, available through Control Panel > System and Security > File History, is used to back up files to an external drive or network location."
Impacted systems display several telltale signs of the malfunction. Event Viewer logs show crash events tied to FileHistory.exe and KERNELBASE.dll. Users encounter persistent "Reconnect your drive" prompts despite having compatible backup drives properly connected and operational. The "Last Backup" timestamp fails to refresh, and previously archived files report "No previous version available" when accessed.
The problem spans multiple Windows editions: Windows 10 version 21H2 and newer, Windows 10 Enterprise LTSC 2016 and 2019 variants, and Windows 11 version 23H2 and newer.
This represents one of several complications stemming from the September 2026 cumulative updates. Microsoft released emergency out-of-band patches seven days prior to address Remote Desktop Services failures, Hyper-V malfunctions, and USB audio defects introduced by the monthly security release. However, the company acknowledged that these expedited fixes did not fully resolve audio-related problems and development teams continue working toward a complete solution.
In a separate incident, Microsoft distributed a temporary workaround for a distinct defect preventing certain Windows 11 users from authenticating with legitimate domain credentials following the September patch deployment.