Troubleshoot Microsoft Defender Antivirus while migrating from a third-party solution

You can find help here if you encounter issues while migrating from a third-party security solution to Microsoft Defender Antivirus.

Review event logs

1. Open the Event viewer app by selecting the Search icon in the taskbar, and searching for event viewer.

   Information about Microsoft Defender Antivirus can be found under Applications and Services Logs > Microsoft > Windows > Windows Defender.

2. From there, select Open underneath Operational.

   Selecting an event from the details pane will show you more information about an event in the lower pane, under the General and Details tabs.

Microsoft Defender Antivirus won’t start

This issue can manifest in the form of several different event IDs, all of which have the same underlying cause.

Associated event IDs

How to tell if Microsoft Defender Antivirus won’t start because a third-party antivirus is installed

On a Windows 10 or Windows 11 device, if you are not using Microsoft Defender for Endpoint, and you have a third-party antivirus installed, then Microsoft Defender Antivirus will be automatically turned off. If you are using Microsoft Defender for Endpoint with a third-party antivirus installed, Microsoft Defender Antivirus will start in passive mode, with reduced functionality.

Use Services app to check if Microsoft Defender Antivirus is turned off

To open the Services app, select the Search icon from the taskbar and search for services. You can also open the app from the command-line by typing services.msc.

Information about Microsoft Defender Antivirus will be listed within the Services app under Windows Defender > Operational. The antivirus service name is Windows Defender Antivirus Service.

While checking the app, you may see that Windows Defender Antivirus Service is set to manual, but when you try to start this service manually, you get a warning stating, The Windows Defender Antivirus Service service on Local Computer started and then stopped. Some services stop automatically if they are not in use by other services or programs.

This indicates that Microsoft Defender Antivirus has been automatically turned off to preserve compatibility with a third-party antivirus.

Generate a detailed report

You can generate a detailed report about currently active group policies by opening a command prompt in Run as admin mode, then entering the following command:

GPresult.exe /h gpresult.html

This will generate a report located at ./gpresult.html. Open this file and you might see the following results, depending on how Microsoft Defender Antivirus was turned off.

Group policy results

If security settings are implemented via group policy (GPO) at the domain or local level, or though System center configuration manager (SCCM)

Within the GPResults report, under the heading, Windows Components/Windows Defender Antivirus, you may see something like the following entry, indicating that Microsoft Defender Antivirus is turned off.

If security settings are implemented via Group policy preference (GPP)

Under the heading, Registry item (Key path: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender, Value name: DisableAntiSpyware), you may see something like the following entry, indicating that Microsoft Defender Antivirus is turned off.

If security settings are implemented via registry key

The report may contain the following text, indicating that Microsoft Defender Antivirus is turned off:

Registry (regedit.exe)

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender DisableAntiSpyware (dword) 1 (hex)

If security settings are set in Windows or your Windows Server image

Your imagining admin might have set the security policy, DisableAntiSpyware, locally via GPEdit.exe, LGPO.exe, or by modifying the registry in their task sequence. You can configure a Trusted Image Identifier for Microsoft Defender Antivirus.

Turn Microsoft Defender Antivirus back on

Microsoft Defender Antivirus will automatically turn on if no other antivirus is currently active. You’ll need to turn the third-party antivirus completely off to ensure Microsoft Defender Antivirus can run with full functionality.

Passive mode is available if you start using Microsoft Defender for Endpoint and a third-party antivirus together with Microsoft Defender Antivirus. Passive mode allows Microsoft Defender Antivirus to scan files and update itself, but it will not remediate threats. In addition, behavior monitoring via Real Time Protection is not available under passive mode, unless Endpoint data loss prevention (DLP) is deployed.

Another feature, known as limited periodic scanning, is available to end-users when Microsoft Defender Antivirus is set to automatically turn off. This feature allows Microsoft Defender Antivirus to scan files periodically alongside a third-party antivirus, using a limited number of detections.