Summary
Attachment Manager helps protect your device by identifying files that were downloaded from the internet or received from other potentially unsafe locations. Windows uses security information, sometimes called Mark of the Web (MOTW), to determine whether a file should display a security warning before it’s opened.
Files downloaded from websites, email messages, or messaging apps might display warnings when you try to open them. This behavior helps protect your device from unsafe files.
How Attachment Manager works
When you download a file, Windows adds information about where the file came from. This information may include whether the file originated from:
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The internet
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Another computer
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A restricted or untrusted location
When you open the file, Windows checks this information and may:
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Display a warning before opening the file
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Block the file from opening automatically
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Apply additional protection in apps such as Microsoft Office or Microsoft Edge
Check whether a file is blocked
If Windows identifies a file as potentially unsafe, you may see a message such as:
“This file came from another computer and might be blocked to help protect this computer.”
To check whether a file is blocked:
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Open File Explorer.
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Locate the file.
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Right-click the file and select Properties.
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On the General tab, look for a security message near the bottom of the window.
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If the file is blocked, select Unblock.
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Select Apply > OK.
Only unblock files from trusted sources.
Open a blocked file safely
Before opening a downloaded file:
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Verify where the file came from.
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Scan the file with Microsoft Defender Antivirus or your antivirus software.
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Make sure the file type matches what you expected to download.
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Avoid opening unexpected email attachments or files from unknown senders.
Manage download protection in Microsoft Edge
Microsoft Edge uses Microsoft Defender SmartScreen to help protect against unsafe downloads and websites.
To manage SmartScreen settings:
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Open Microsoft Edge.
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Select Settings and more (...) > Settings.
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Select Privacy, search, and services.
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Under Security, turn Microsoft Defender SmartScreen on or off.
Turning off SmartScreen can make your device more vulnerable to malicious files and websites.
Why Office files may open in Protected View
Microsoft Office apps may open downloaded files in Protected View to help prevent malicious content from running automatically.
Files from untrusted locations may:
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open in read-only mode
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disable editing
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disable macros or active content
If you trust the file and need to edit it, select Enable Editing in the Office app.
Troubleshoot warnings for downloaded files
If you continue to receive warnings for trusted files:
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Make sure Windows and your apps are up to date.
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Verify that the file came from a trusted source.
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Re-download the file if it may have been corrupted.
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Check whether your organization applies security policies that block downloaded files.
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Temporarily disable third-party download managers or security software only for testing purposes.
Advanced steps:
IT administrators can manage Attachment Manager behavior through:
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Group Policy
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Microsoft Defender settings
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SmartScreen policies
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file attachment handling policies
Changes to these settings can affect how Windows handles downloaded files and internet-based content.
Editing security policies or the registry incorrectly can cause system issues. These changes should only be made by advanced users or IT administrators.
