Dangerous Downloaded And Or Installed Ones?

Different security products can react at different stages of the same download or file, so the behavior on screen can look inconsistent even when protection is working.

Key reasons this can happen:

1. Microsoft Edge and Microsoft Defender protect at different points
   • Microsoft Edge can allow a file to download, warn about it, interrupt it, or let it continue based on file type, user gesture, site history, and Microsoft Defender SmartScreen results.
   • For potentially dangerous file types, Edge may block or interrupt the download if it lacks the required user gesture. In that case, the download shows as blocked and can be kept or deleted.
2. A downloaded file is not the same as an executed file
   • Windows can mark downloaded files with security information from the internet using Attachment Manager and Mark of the Web.
   • That can cause a warning or block when the file is opened, even if the file was downloaded successfully.
3. Microsoft Defender may detect at execution, open, or scan time
   • Microsoft Defender checks files and apps that are downloaded and installed, and can also scan files already on the system.
   • If a file is never opened or executed, it may not cause harm. One accepted Microsoft Q&A answer states that if the file was never opened or executed and Defender removed it, there is no reason to worry.
4. Another antivirus may be more aggressive at download time
   • Some antivirus products block earlier in the chain, such as during the browser download itself, while Microsoft protections may warn, mark, quarantine, or block later depending on the file, source, and behavior.
   • That difference does not by itself prove that one product is failing.
5. Running multiple real-time antivirus products can cause conflicts
   • Microsoft recommends not running other antivirus or antispyware products at the same time as Windows Defender.
   • Using more than one real-time security product can affect performance and can also cause update or install errors.

If dangerous files are fully downloading and installing with no detection at all, that is not expected behavior. A Microsoft Q&A accepted answer states that Defender removed EICAR test files immediately, and if that is not happening, something may be wrong with the installation.

Practical checks:

1. In Windows Security: Start > Settings > Update & Security > Windows Security > Virus & threat protection.
2. Select Manage settings and confirm Real-time protection is on.
3. For better protection, turn on Cloud-delivered protection and Automatic sample submission.
4. In Microsoft Edge: Settings and more (...) > Settings > Privacy, search, and services > under Security, confirm Microsoft Defender SmartScreen is on.
5. Right-click a downloaded file in File Explorer > Properties and check whether Windows shows it as blocked.
6. Avoid running another real-time antivirus alongside Defender. If another product is installed, uninstall the previous security software first.
7. Run an on-demand scan with Microsoft Safety Scanner if malware is suspected.

Caution: turning off Microsoft Defender Antivirus or SmartScreen can make the device more vulnerable to malicious files and websites.

References:

• Identify and interrupt downloads of potentially dangerous files
• Information about the Attachment Manager in Microsoft Windows
• Getting started with Microsoft Defender
• Antivirus and antimalware software: FAQ
• 20 Eicar Test Files Fully Downloaded End Results? - Microsoft Q&A
• Somehow downloaded Trojan:Win32/Malgent without opening it. Should I be worried now? - Microsoft Q&A