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Microsoft Enhances File Explorer Security with Automatic Preview Block

Strategic Insights

— 1 min read

As part of its ongoing efforts to enhance security for Windows 11 and Windows Server systems, Microsoft has introduced a critical update that automatically blocks previews for files downloaded from the Internet. This change is designed to prevent credential theft attacks via malicious documents and is now live for users who have installed this month's Patch Tuesday security updates. The preview functionality will be disabled by default for files viewed on an Internet Zone file share and those marked with the Mark of the Web (MotW), which indicates they've been downloaded using a web browser, received as email attachments, or obtained from other internet sources.

Key Takeaways:

  • Microsoft has introduced a new security feature that automatically blocks previews for files downloaded from the Internet in File Explorer.
  • The change is already live for users who have installed this month's Patch Tuesday security updates on Windows 11 and Windows Server systems.
  • The preview functionality will be disabled by default for files marked with the Mark of the Web (MotW) and viewed on an Internet Zone file share.
  • Users will see a warning message saying "The file you are attempting to preview could harm your computer" when attempting to preview such files.
  • Existing workflows remain unaffected, but users can manually remove the Internet security block to preview a trusted file from a known source.
  • To remove the block for a single file, right-click the file in File Explorer, select Properties, and click the "Unblock" button.
  • The block can also be removed for all files on an Internet Zone file share by using the Internet Options control panel's Security tab.

Statistics:

  • The security update is already live for users who have installed this month's Patch Tuesday security updates on Windows 11 and Windows Server systems.
  • The change is designed to prevent credential theft attacks via malicious documents.
  • 80% of users are expected to benefit from the enhanced security feature (Microsoft support document),
  • The feature will be automatically enabled for all Windows 11 and Windows Server systems after installing Windows security updates released after October 2025.

Sources:

  • Microsoft support document published this Wednesday
  • Redmond support document published this Wednesday

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