Norton Scan Not Detecting a Virus – How Can I Troubleshoot It?

Deery Marteem 0 Reputation points
2026-10-08T13:53:08.66+00:00

Update the security software first. If updates are failing, possible causes include malware disabling the antivirus, malware blocking access to the internet or security sites, Windows Update problems, or using an unsupported version of Windows. Try manually installing the latest updates.

Run another scan after reducing system load. Close unnecessary apps before scanning. Restarting the PC and running the scan immediately can help. Full scans can take a long time, especially on large disks or when many archive files such as ZIP files are present.

Make sure there is enough free disk space. Security tools need disk space to remove and quarantine malware. Low free space, especially on drive C, can prevent complete removal.

If malware keeps returning after removal, run Microsoft Defender Offline. This can detect threats that hide while Windows is running. In Windows, go to Start > Settings > Update & Security > Windows Security > Virus & threat protection > Scan options > Windows Defender Offline scan > Scan now. Save work first because the PC restarts before the scan.

If scan errors continue, run Windows Update and install the latest protection updates manually if needed.

If another antivirus product is installed, it can interfere with scanning. Third-party antivirus apps can take over and block Windows Security scanning. If that applies, uninstall the third-party antivirus first, then run a Microsoft Defender scan from Start > Settings > Privacy & security > Windows Security > Virus & threat protection and choose Quick scan or Scan options for Full scan, Custom scan, or Microsoft Defender Offline scan.

If malware changed the system and cleanup is no longer enough, reset or restore the PC. Back up files first. Restore from backups created before the infection when possible, because backups stored on the PC during infection might also be affected.

If the issue is specifically that Norton is missing a threat, the supported troubleshooting in the available guidance is to update definitions, check for interference from other security software, and use Microsoft Defender Offline if the infection keeps reinstalling itself.

Windows for home | Windows 10 | Security and privacy
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  1. AI answer

    2026-10-08T13:53:30.7633333+00:00

    For a Windows 10 home PC, the supported troubleshooting steps are:

    1. Update security intelligence first In Windows Security under Virus & threat protection, use Check for updates to get the latest security intelligence. If updates fail, possible causes include malware disabling antivirus, malware blocking internet or security sites, Windows Update problems, or an unsupported version of Windows. Manual installation of the latest updates is also supported.
    2. Reduce system load and run the scan again Close non-essential apps before scanning. Restarting the PC and running the scan immediately can help. Full scans can take a long time, especially on large disks or when many archive files such as ZIP files are present.
    3. Make sure there is enough free disk space Microsoft Defender Antivirus needs disk space to remove and quarantine malware. Low free space, especially on the system drive, can prevent complete removal.
    4. Check for antivirus interference If another antivirus product is installed, it can interfere with Windows Security scanning. Third-party antivirus software can take over and block Virus & threat protection. If that applies, uninstall the third-party antivirus, then run a Microsoft Defender scan from: Start > Settings > Privacy & security > Windows Security > Virus & threat protection Then choose Quick scan or Scan options for Full scan, Custom scan, or Microsoft Defender Offline scan.
    5. If malware keeps coming back, run Microsoft Defender Offline This is recommended when malware may be reinstalling itself after restart. Go to: Start > Settings > Update & Security > Windows Security > Virus & threat protection > Scan options > Windows Defender Offline scan > Scan now Save work first because the PC restarts before the offline scan begins.
    6. If cleanup is incomplete If a threat is only partially removed, run the Malicious Software Removal Tool:
      • Press Windows key + R
      • Type %windir%\system32\mrt.exe
      • Select OK
      • Allow the app to make changes if prompted, then follow the scan and cleanup prompts
      After that, restart the PC and manually install the latest updates.
    7. If malware caused irreversible system changes Reset, restore, or reinstall Windows. Back up files first. Restore from backups created before the infection when possible, because backups stored on the PC during infection might also be affected.

    If the issue is specifically that Norton is missing a threat, the supported guidance available here is to update definitions, reduce scan interference, ensure enough disk space, and use Microsoft Defender Offline if the infection keeps reinstalling itself.

    AI-generated content may be incorrect. Read our transparency notes for more information.

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