Possible reasons Microsoft Defender may report threats that Norton doesn't

There are a few reasons why Microsoft Windows Defender may find certain threats or unwanted applications that Norton does not report.

Microsoft Windows Defender may report a file that has already been quarantined by Norton. While this may be initially alarming, files quarantined by Norton pose no risk to your computer. Threats are stored in quarantine in the rare event that a user needs to reverse actions taken by Norton.
The file detected by Defender may not be a genuine threat even though it was reported by Microsoft as one. These kinds of files are known as False Positives. One explanation for a false positive is that Microsoft Windows Defender may not have enough information about the file to determine that it is safe. Norton has an enormous database of file and URL reputations gathered from millions of computer systems around the world. In 2015, Norton identified 430 million new unique pieces of malware. For more information, read View or change the Norton trust level of files that you use.

Submit the detected file to Microsoft.
Norton security research centers around the world provide unparalleled analysis and protection from IT security threats that include malware, security risks, vulnerabilities, and spam.
Thousands of new viruses, Trojans, and worms are created every day. It is possible that Microsoft has recognized a threat which Norton does not yet recognize. Keep in mind that Norton has multiple layers of protection. It is possible Norton has not yet recognized a threat at the time Defender recognizes it (for example during the download) but will catch it before it begins to harm your computer.

If you come across a file that Microsoft Windows Defender has detected as a threat but the Norton product has not, you can submit the file to Norton Security Response. For more information, read Submit a file to Norton.

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