The September Windows Update Broke File History — And Nobody Noticed

What happened

On September 8, 2026, Windows installed a routine security update on millions of PCs. For people relying on File History — Windows’ built-in file backup — that update quietly stopped their backups from being created or updated. The problem isn’t really that a bug happened. Bugs happen. The problem is that for two weeks, many people had no idea they were unprotected.

Microsoft acknowledged the issue in a service alert on September 22. After the September 2026 security updates (KB5124008 on current Windows 11 builds, with equivalent updates on Windows 10), File History could no longer create or update backups on affected systems — Windows 11 version 23H2 and later, and Windows 10 version 21H2 and later.

The symptoms were almost designed to be missed:

• “Reconnect your drive” alerts appeared even when the backup drive was connected and working fine.
• The “Last Backup” timestamp stopped updating — but you had to look for it to notice.
• Previously backed-up files started showing “No previous version available.”
• In some cases, Event Viewer recorded crash events referencing FileHistory.exe and KERNELBASE.dll.

In other words, the tool that’s supposed to catch your mistakes made its own mistake and hid it. A user who trusted their backup was fine had roughly two weeks of file changes — new documents, edited photos, downloaded receipts — that existed in exactly one place.

The fix (and who still waits)

Update, October 13, 2026: Today’s Patch Tuesday update (KB5127648 for Windows 11 24H2/25H2/26H2, KB5126653 for Windows 11 23H2, KB5127646 for 26H1, and the October cumulative update for Windows 10) carries the File History fix to everyone — including Windows 10 users, who never got the optional September preview fix. Install this month’s update, then check File History’s “Last Backup” timestamp; if it’s still stale, the backup is still telling you something is wrong. (On Windows 11 23H2 Home/Pro — which no longer receives updates — upgrading is the only fix. Note this is also the last update for Windows 11 24H2 Home/Pro: let Windows Update move you to 25H2 or 26H2.) One more reason to verify rather than trust: early testers of the fix reported the “Run now” button staying glitchy, so confirm with an actual restore, not just the timestamp.

By late September, Microsoft shipped fixes in optional updates: KB5124010 for Windows 11 versions 24H2 and 25H2, and KB5124006 for 26H1. Those updates don’t install on their own. You have to go to Settings → Windows Update → Advanced options → Optional updates and install them manually. Everyone else got the fix in the October 13 Patch Tuesday release.

Practical steps, right now:

1. Open Settings → Windows Update → Advanced options → Optional updates and install any update that mentions File History.
2. After updating, check File History’s “Last Backup” timestamp. It should be current. If it isn’t, that’s your backup telling you something is wrong — listen to it.
3. Test a restore. Pick an unimportant file, restore an older version of it, and confirm the contents are right. A backup you haven’t tested is a hope, not a plan.

The real lesson: silent failure is the enemy

The bug will be forgotten by November. The pattern won’t be, because this wasn’t File History’s first stumble. It ships off by default — most people who think they’re backed up by Windows aren’t backed up by anything. When it does run, its status is buried in a Control Panel page most people never open. And restores routinely confuse people: which version is which, where did it go, why is the file I deleted last week not there.

None of that is a conspiracy. It’s what happens when backup is a checkbox feature inside an operating system with ten thousand other priorities. The feature that keeps you safe needs to be loud when it works and louder when it doesn’t.

That suggests a checklist for whatever protects your files, built-in or not:

• It tells you plainly when a run succeeded or failed. Not a cryptic message, not a stale timestamp — a clear result, every run.
• It backs up what you actually care about. File History defaults to the user profile folders (Documents, Music, Pictures, Videos, Desktop). That’s a reasonable default, but if your important files live elsewhere, the default isn’t protecting them. (See also: File Backup vs. System Image — which one do you actually need?)
• Restoring one file is obvious. You don’t need your whole system back — you need the spreadsheet from Tuesday. The restore path should be shorter than the backup setup.
• It doesn’t depend on the same machine’s good mood. An OS update should not be able to silently disable your backups. A backup tool independent of the operating system’s built-in components is not vulnerable to this particular class of failure. Keeping a disconnected copy matters too — here’s how to protect your backups from ransomware.

How BackupEasy helps

A file backup that survives Windows updates

BackupEasy was built around the checklist above, because the September bug is exactly the kind of failure it was designed to avoid:

• A Windows update can’t switch it off. It isn’t part of Windows — it’s a separate tool — so an OS patch can’t silently disable your backups the way KB5124008 disabled File History.
• Every run reports plainly. You get a clear result after each run: what was copied, and whether anything went wrong. No stale timestamps to squint at.
• You choose the folders. Not just the profile defaults — any source folder you point it at, from C:\Users\Demo\Documents to a projects directory on another drive.
• One-file restore is the main path. Pick the file, get it back exactly as it was. The restore takes less time than the setup.
• Fully offline. No account, no cloud upload. Your files never leave your own drives.
• $19.99 once, with a 60-day free trial. Confirm it runs before you spend anything. The 5-PC household pack is $29.99.

That isn’t an argument against File History, which is fine as a second layer once it’s fixed and actually running. It’s the same lesson the September bug teaches: the backup you check is the backup you trust, and the backup you trust is the one simple enough that you actually verify it.

Related: BackupEasy: Five Backup Jobs, One Simple Tool

The five-minute audit

Whether you use File History, BackupEasy, or something else entirely, take five minutes today:

1. When did your last backup actually complete? Not when it was scheduled — when it finished successfully.
2. Restore one file and read it. If the contents are right, your backup is real. If you can’t find the file, you just learned something important for free.
3. Know where the “it broke” signal lives. If your backup can fail without telling you, it will eventually do exactly that, and you’ll discover it on the worst possible day.

The September bug was embarrassing for Microsoft and fixable with a patch. The habit it exposed — trusting a backup you’ve never checked — doesn’t fix itself. Check yours.