Is Your File Preview Not Working After a Recent Windows Update?

Is your file preview not working after a recent Windows update?

You can run a script on the entire computer/server and wait 5 minutes for it to finish, OR you can fix the folder you are working on in one second.

Open File Explorer and go to your folder. In a blank space, right-click. Choose Open in Terminal (or PowerShell). Copy and paste the text below, then hit Enter. Close the shell window.

dir | Unblock-File

Files are now unlocked in this folder. Preview works again.

The "Mark of the Web" Headache: Why Your File Previews Are Breaking

If you're an accountant or attorney, your day is a constant stream of client-sent PDFs, spreadsheets, and documents. Recently, you may have noticed a frustrating change: clicking a file in Windows File Explorer no longer shows a preview. Instead, you get a blunt warning: "The file you are attempting to preview could harm your computer."

This isn't a bug. It's a security feature called Mark of the Web (MOTW), and it's currently slowing down professional workflows everywhere.

What is MOTW?

MOTW is a digital "tag" Windows attaches to any file originating from the internet — including email attachments from Outlook, downloads from client portals, or files from Slack. Starting with the October 2025 security updates, Microsoft began blocking the "Preview Pane" for any file carrying this tag.

Why is this happening?

Cybercriminals discovered they could steal your Windows login credentials (specifically your NTLM hashes) just by getting you to preview a malicious file. You didn't even have to open it; just clicking it once to see the preview was enough to leak your data. Microsoft's "fix" was to disable previews for all untrusted external files by default.

How to Fix It

While the security risk is real, the loss of productivity is a major hurdle. Here are three ways to get your previews back:

• The Individual Fix: Right-click the file > Properties. In the General tab, check the Unblock box at the bottom and hit Apply.
• The Bulk Fix: If you have a folder full of client documents, you can unblock them all at once using PowerShell. Run this command:
  
  Get-ChildItem -Path "C:YourClientFolder" -Recurse | Unblock-File
• The Permanent Fix (For IT): If you use a specific network drive or SharePoint site, add that location to your "Trusted Sites" in Windows Internet Options. Files saved from trusted zones won't get the MOTW tag.

NOTE: At this time, we cannot permanently disable MOTW. We have to learn to live with it, and/or work around it.

We have scripts to clear an entire computer or server of the MOTW marking, even ones we can run periodically to scan in the background. If you need one of these scripts, reach out. Even if you are a competitor, we are glad to help.

Tip: Only unblock files from sources you explicitly trust. If a file looks suspicious, that preview block is your first line of defense.