{"id":79925,"date":"2025-12-05T19:29:57","date_gmt":"2025-12-05T13:59:57","guid":{"rendered":"http:\/\/198.58.113.91\/blog\/?p=79925"},"modified":"2025-12-06T17:33:03","modified_gmt":"2025-12-06T12:03:03","slug":"file-explorer-previews-blocked-harm-your-computer","status":"publish","type":"post","link":"https:\/\/www.winhelponline.com\/blog\/file-explorer-previews-blocked-harm-your-computer\/","title":{"rendered":"File Explorer: The file you are attempting to preview could harm your computer"},"content":{"rendered":"<p>After installing the October 15 (2025), cumulative update for Windows 11, File Explorer turns off the preview feature for files downloaded from the internet. After the October 2025 or a later Windows security update is installed, the File Explorer preview pane will display the following message:<\/p>\n<pre class=\"err\">The file you are attempting to preview could harm your computer. If you trust the file and the source you received it from, open it to view its contents.\r\n<\/pre>\n<p><!--more--><\/p>\n<h2>Cause<\/h2>\n<p>This change of behavior applies to files marked with Mark of the Web (MotW) after download from the internet, and to files viewed on an Internet Zone file share. This is a security measure that prevents a vulnerability that could leak NTLM hashes when users preview potentially unsafe files. For more details, review the following frequently asked questions about this change.<\/p>\n<ul>\n<li><a href=\"https:\/\/support.microsoft.com\/en-us\/topic\/file-explorer-automatically-disables-the-preview-feature-for-files-downloaded-from-the-internet-56d55920-6187-4aae-a4f6-102454ef61fb\" target=\"_blank\" rel=\"noopener\">File Explorer automatically disables the preview feature for files downloaded from the internet &#8211; Microsoft Support<\/a><\/li>\n<li><a href=\"https:\/\/support.microsoft.com\/en-us\/topic\/october-14-2025-kb5066835-os-builds-26200-6899-and-26100-6899-1db237d8-9f3b-4218-9515-3e0a32729685\" target=\"_blank\" rel=\"noopener\">October 14, 2025\u2014KB5066835 (OS Builds 26200.6899 and 26100.6899) &#8211; Microsoft Support<\/a><br \/>\n<blockquote><p>[File Explorer] After installing this update, File Explorer automatically disables the preview feature for files downloaded from the internet. This change is designed to enhance security by preventing a vulnerability when users preview potentially unsafe files.<\/p><\/blockquote>\n<\/li>\n<\/ul>\n<hr \/>\n<h2>Resolution<\/h2>\n<h3>Option 1: Unblock each file using the Properties dialog<\/h3>\n<p>If you trust the source of the file you want to preview, unblock the file. To remove the block for a downloaded file, right-click the file in File Explorer, select Properties, select <strong>Unblock<\/strong>, and click OK.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-79928\" src=\"https:\/\/www.winhelponline.com\/blog\/wp-content\/uploads\/2025\/12\/unblock-file-properties.jpg\" alt=\"Unblock file using Properties- MoTw. NTFS\" width=\"386\" height=\"148\" \/><\/p>\n<h3>Option 2: Bulk unblock downloaded files using PowerShell or Streams.exe<\/h3>\n<p>If you have many downloaded files and want to unblock them en masse (i.e., bulk unblock), you can use Microsoft&#8217;s Streams.exe tool or PowerShell. Please check out the following article for more information:<\/p>\n<p><a href=\"https:\/\/www.winhelponline.com\/blog\/bulk-unblock-files-downloaded-internet\/\">How to Bulk Unblock Files Downloaded from the Internet<\/a><\/p>\n<div class=\"qt\">\n<h4>What about files in a network share? I can&#8217;t unblock them.<\/h4>\n<p><strong>Note:<\/strong> To remove the block for files on a file share, use the Internet Options control panel&#8217;s Security tab to add the file share&#8217;s address to either the Local intranet or Trusted sites security zone.<\/p>\n<p>To launch the Internet Options dialog, press Win + R, type <code><strong>inetcpl.cpl<\/strong><\/code> and click OK. Select the &#8220;Security&#8221; tab, and click Trusted sites. Click &#8220;Sites&#8221; and add the website or UNC share path (which hosts the files) there.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-79926\" src=\"https:\/\/www.winhelponline.com\/blog\/wp-content\/uploads\/2025\/12\/ie-trusted-zone-sites.png\" alt=\"Internet Explorer options - Trusted sites zone\" width=\"385\" height=\"350\" \/><\/p>\n<\/div>\n<h3>Option 3: Move the files to a FAT32 disk and then move them back<\/h3>\n<p>Saving downloaded files to a FAT32 partition should workaround the problem. Mark of the Web (MotW) is not saved when you save the files to a non-NTFS (e.g, FAT32) partition. If you have hundreds of files, you can move them to a FAT32 disk and then move them back to the original location. That way, you erase the NTFS ADS data, where MotW is stored.<\/p>\n<hr \/>\n<h2>Workaround<\/h2>\n<p><strong>To turn on Previews back on regardless of file source and without having to unblock each file<\/strong>, you may use the IE zones registry workaround by Eric Lawrence of the Microsoft Web Defense team. Please create a System Restore point and employ the registry edit here.<\/p>\n<p><a href=\"https:\/\/gist.github.com\/ericlaw1979\/1b7239ae22a9fe4ecf7c396255bff259\" target=\"_blank\">Turn Shell Previews back on regardless of file source &#8211; GitHub<\/a><\/p>\n<pre>Windows Registry Editor Version 5.00\r\n\r\n[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Internet Settings\\Zones\\3]\r\n\"180F\"=dword:00000000\r\n<\/pre>\n<div class=\"qt\">\n<strong>Important<\/strong>: Note the caveat mentioned on that link. It suggests disabling NTLM over SMB if you apply that registry edit.<br \/>\nQuoting Eric Lawrence:<\/p>\n<blockquote><p>Warning, this exposes you to the risk of NTLM hash leaks: https:\/\/textslashplain.com\/2019\/10\/09\/navigating-to-file-urls\/#:~:text=to%20Edge%2095%2B.-,What%E2%80%99s%20the%20Risk%3F,-The%20most%20obvious<\/p>\n<p>You should disable NTLM over SMB to address that risk: <code><strong>Set-SMbClientConfiguration -BlockNTLM $true<\/strong><\/code> from PowerShell.\n<\/p><\/blockquote>\n<p>To accomplish the above task using command-line, run these commands from admin Command Prompt.<\/p>\n<pre class=\"cmd\">\r\nreg.exe add \"HKLM\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Internet Settings\\Zones\\3\" \/v 180F \/d 0 \/t REG_DWORD \/f\r\n\r\nPowerShell.exe -Command \"& {Set-SMbClientConfiguration -BlockNTLM $true}\r\n<\/pre>\n<p><em>Reference: <a target=\"_blank\" href=\"https:\/\/learn.microsoft.com\/en-us\/windows-server\/storage\/file-server\/smb-ntlm-blocking?tabs=powershell\">Block NTLM connections on SMB in Windows Server 2025 | Microsoft Learn<\/a><\/em><\/p>\n<\/div>\n<p>The <strong>180F<\/strong> registry value corresponds to the following security zone setting:<\/p>\n<pre>Allow previewing and custom thumbnails of OpenSearch query results in Windows Explorer<\/pre>\n<p>The above setting is <strong>not<\/strong> displayed in the user interface in Internet Explorer Options (inetcpl.cpl)<\/p>\n<p><em><strong>Reference:<\/strong> <a href=\"https:\/\/learn.microsoft.com\/en-us\/previous-versions\/troubleshoot\/browsers\/security-privacy\/ie-security-zones-registry-entries\" target=\"_blank\" rel=\"noopener\">IE security zones registry entries for advanced users &#8211; Internet Explorer | Microsoft Learn<\/a><\/em><\/p>\n<hr \/>\n<h3>References<\/h3>\n<p><a href=\"https:\/\/textslashplain.com\/2025\/10\/20\/windows-shell-previews\/\" target=\"_blank\" rel=\"noopener\">Windows Shell Previews \u2013 Restricted \u2013 text\/plain<\/a><\/p>\n<p><a href=\"https:\/\/www.winhelponline.com\/blog\/bulk-unblock-files-downloaded-internet\/\">How to Bulk Unblock Files Downloaded from Internet<\/a><\/p>\n<p><a href=\"https:\/\/learn.microsoft.com\/en-us\/previous-versions\/troubleshoot\/browsers\/security-privacy\/ie-security-zones-registry-entries\" target=\"_blank\" rel=\"noopener\">IE security zones registry entries for advanced users &#8211; Internet Explorer | Microsoft Learn<\/a><\/p>\n<p><a href=\"https:\/\/kb.foxit.com\/s\/articles\/How-to-Solve-the-Issue-That-File-Explorer-Is-Unable-to-Preview-PDF-Files-and-Displays-the-Warning-The-file-you-are-attempting-to-preview-could-harm-your-computer-If-you-trust-the-file-and-the-source-you-received-it-from-open-it-to-view-its-contents\" target=\"_blank\" rel=\"noopener\">How to Solve the Issue That File Explorer Is Unable to Preview PDF Files and Displays the Warning<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>After installing the October 15 (2025), cumulative update for Windows 11, File Explorer turns off the preview feature for files downloaded from the internet. After the October 2025 or a later Windows security update is installed, the File Explorer preview pane will display the following message: The file you are attempting to preview could harm &#8230; <a title=\"File Explorer: The file you are attempting to preview could harm your computer\" class=\"read-more\" href=\"https:\/\/www.winhelponline.com\/blog\/file-explorer-previews-blocked-harm-your-computer\/\" aria-label=\"Read more about File Explorer: The file you are attempting to preview could harm your computer\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[869],"tags":[191,441],"class_list":["post-79925","post","type-post","status-publish","format-standard","hentry","category-windows-11","tag-error-messages","tag-registry"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":80266,"url":"https:\/\/www.winhelponline.com\/blog\/enable-preview-of-log-files-explorer\/","url_meta":{"origin":79925,"position":0},"title":"How to Enable Preview of .LOG Files in File Explorer","author":"Ramesh","date":"February 16, 2026","format":false,"excerpt":"By default, the preview capability exists for most text-based files in File Explorer. However, for some file types, such as .log or .py, a preview may not be generated by default and you see the message \"No preview available\" in the preview pane in File Explorer. You can enable preview\u2026","rel":"","context":"In &quot;Windows 10&quot;","block_context":{"text":"Windows 10","link":"https:\/\/www.winhelponline.com\/blog\/category\/microsoft\/windows\/windows-10\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":6431,"url":"https:\/\/www.winhelponline.com\/blog\/eml-file-preview-pane-explorer-windows\/","url_meta":{"origin":79925,"position":1},"title":"How to Enable Preview of .eml (Email Message) Files in Explorer","author":"Ramesh","date":"August 6, 2018","format":false,"excerpt":"Many users of Windows Mail or Windows Live Mail (part of Windows Live Essentials) used to backup individual emails and save them as .EML files. Since Windows Live Mail has been discontinued,\u00a0users are forced to use third-party mailers or even buy Microsoft's own produce, Microsoft Outlook. However, the preview pane\u2026","rel":"","context":"In &quot;Utilities&quot;","block_context":{"text":"Utilities","link":"https:\/\/www.winhelponline.com\/blog\/category\/utilities\/"},"img":{"alt_text":".eml file no preview available","src":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2018\/08\/eml-preview-0.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2018\/08\/eml-preview-0.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2018\/08\/eml-preview-0.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2018\/08\/eml-preview-0.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":309,"url":"https:\/\/www.winhelponline.com\/blog\/enable-or-disable-thumbnail-preview-for-pdf-files\/","url_meta":{"origin":79925,"position":2},"title":"[Fix] PDF Thumbnail and Preview Not Showing Up in File Explorer","author":"Ramesh","date":"May 29, 2008","format":false,"excerpt":"In your Windows computer, File Explorer may not display PDF thumbnails, and instead, show only the default icon assigned for PDF files. This might happen even if you have the option Always show icons, never thumbnails unchecked in the View tab of the Folder Options dialog. Also, in Microsoft Outlook\u2026","rel":"","context":"In &quot;Microsoft Edge&quot;","block_context":{"text":"Microsoft Edge","link":"https:\/\/www.winhelponline.com\/blog\/category\/edge\/"},"img":{"alt_text":"Edge PDF Preview Handler - Microsoft PDF Previewer","src":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/05\/edge-preview-handler.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/05\/edge-preview-handler.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/05\/edge-preview-handler.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/05\/edge-preview-handler.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":24403,"url":"https:\/\/www.winhelponline.com\/blog\/disable-preview-pane-file-types-explorer\/","url_meta":{"origin":79925,"position":3},"title":"How to Disable Preview for Certain File Types in Explorer Preview Pane","author":"Ramesh","date":"October 15, 2021","format":false,"excerpt":"The preview pane in File Explorer shows you the preview for various file types in Windows 10 and Windows 11. Windows comes with a built-in set of preview handlers. In addition, third-party applications add their own handlers that can generate previews for their proprietary file types. Windows allows you to\u2026","rel":"","context":"In &quot;Utilities&quot;","block_context":{"text":"Utilities","link":"https:\/\/www.winhelponline.com\/blog\/category\/utilities\/"},"img":{"alt_text":"disable preview for selected file type","src":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2021\/10\/disable-preview-pane-file-type-0.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2021\/10\/disable-preview-pane-file-type-0.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2021\/10\/disable-preview-pane-file-type-0.png?resize=525%2C300&ssl=1 1.5x"},"classes":[]},{"id":29386,"url":"https:\/\/www.winhelponline.com\/blog\/preview-pane-blank-every-file-type\/","url_meta":{"origin":79925,"position":4},"title":"Preview Pane is Blank for Every File Type Except Images","author":"Ramesh","date":"October 21, 2022","format":false,"excerpt":"We've seen the \"No preview available\" situations before, caused by the incorrect or missing preview handler registration for a file type. Here is a similar problem: the preview pane is empty, showing just the white space for all file types except images. However, the image file types may preview correctly.\u2026","rel":"","context":"In &quot;Windows 10&quot;","block_context":{"text":"Windows 10","link":"https:\/\/www.winhelponline.com\/blog\/category\/microsoft\/windows\/windows-10\/"},"img":{"alt_text":"preview pane blank white all file types","src":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2022\/10\/preview-pane-blank-white-2.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2022\/10\/preview-pane-blank-white-2.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2022\/10\/preview-pane-blank-white-2.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2022\/10\/preview-pane-blank-white-2.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":182,"url":"https:\/\/www.winhelponline.com\/blog\/fix-thumbnail-preview-for-pictures-w7-vista\/","url_meta":{"origin":79925,"position":5},"title":"Fix: Thumbnails Not Showing up in File Explorer","author":"Ramesh","date":"April 14, 2008","format":false,"excerpt":"Are your image files showing up with a generic mountain and lake scene instead of the miniature or thumbnail display in File Explorer? And video files may show up with a generic icon\/thumbnail. This article tells you how to enable thumbnails in File Explorer on Windows 10\/11 and earlier. RELATED:\u2026","rel":"","context":"In &quot;Windows&quot;","block_context":{"text":"Windows","link":"https:\/\/www.winhelponline.com\/blog\/category\/microsoft\/windows\/"},"img":{"alt_text":"thumbnails blank -- fix the IconServiceLib registry setting","src":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/04\/iconservicelib-registry-thumbnail-fix.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/04\/iconservicelib-registry-thumbnail-fix.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/04\/iconservicelib-registry-thumbnail-fix.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.winhelponline.com\/blog\/wp-content\/uploads\/2008\/04\/iconservicelib-registry-thumbnail-fix.png?resize=700%2C400&ssl=1 2x"},"classes":[]}],"_links":{"self":[{"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/posts\/79925","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/comments?post=79925"}],"version-history":[{"count":0,"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/posts\/79925\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/media?parent=79925"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/categories?post=79925"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.winhelponline.com\/blog\/wp-json\/wp\/v2\/tags?post=79925"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}