Blocked by Windows Defender SmartScreen

Windows Defender SmartScreen is blocking or warning on the installer because it has low or unknown reputation, not necessarily because it is malicious.

SmartScreen evaluates downloads and installers using reputation-based checks:

1. Site and URL reputation
   • SmartScreen checks the download URL against dynamic lists of reported phishing and malicious sites.
   • If the hosting site or URL has poor or no reputation, SmartScreen may show a warning even if the file itself is not known to be malware.
2. File reputation ("not commonly downloaded")
   • SmartScreen checks downloaded files against:
     • A list of known malicious software and unsafe programs.
     • A list of files that are well known and downloaded frequently.
   • If the installer is new, not widely downloaded, or signed in an inconsistent way, SmartScreen may classify it as "unknown" and show a blue warning that the app "isn't commonly downloaded" or "might be risky".
   • This is especially common for:
     • New versions of software.
     • Custom or niche business applications.
     • Large installers hosted on less-popular domains.
3. Behavior and other signals
   • SmartScreen also considers download history, past antivirus results, and URL reputation to decide whether to warn.

What users see

• For known malicious files or URLs, SmartScreen shows a strong block page and clearly states the file/site is unsafe.
• For unknown or low-reputation files, SmartScreen shows a softer warning (blue or less severe) advising caution but still allowing users to proceed.

What can be done from the developer/company side Based on the provided information, there is no direct "whitelist" program for developers to submit installers just to avoid SmartScreen warnings. Instead:

1. Use consistent, trusted code signing
   • Sign all executables and installers with a digital certificate issued by a trusted root authority.
   • Use the same certificate consistently across releases.
   • Over time, SmartScreen can build reputation for the signed publisher and the files.
2. Build reputation over time
   • As more users download and run the installer without it being flagged as malicious, SmartScreen reputation improves.
   • Popular, frequently downloaded files with clean history will eventually install without warnings.
3. Ensure the installer does not include unwanted or bundled software
   • If the installer bundles software that meets criteria for unwanted software, it may be classified negatively. Review the criteria for unwanted applications and avoid bundling anything that could be considered PUA.
4. Verify hosting and distribution practices
   • Host installers on reputable domains and over HTTPS.
   • Avoid third-party download sites that may be associated with malware or unwanted software.
5. If the software is incorrectly detected as malware (not just "unknown")
   • If SmartScreen or Defender classifies the installer as malicious, submit the file as a software developer for analysis and dispute the detection if necessary. Wait for the final determination and use the developer contact form if the result is unsatisfactory.

What can be done for end users

• Users can bypass SmartScreen warnings for unknown but not malicious files by choosing the "Keep" / "Keep anyway" options in Microsoft Edge or by choosing to continue in App Installer, but this is not recommended unless they trust the source.
• Enterprise admins can configure SmartScreen policies (for example, to prevent or allow bypassing warnings) via Group Policy or MDM, but this affects managed environments rather than changing the file’s reputation.

In summary, the warnings appear because the installers currently have low or unknown reputation in SmartScreen’s cloud service. The long-term solution is to:

• Sign the installers with a trusted, consistent certificate.
• Distribute them from reputable locations.
• Allow reputation to build as more users download and run the software without security issues.

References:

• Microsoft Defender SmartScreen
• Microsoft Edge support for Microsoft Defender SmartScreen
• App Installer Security Features
• Available Microsoft Defender SmartScreen settings
• Software developer FAQ