Microsoft Defender AV must be configured to run and scan for malware and other potentially unwanted software.

This policy setting turns off Microsoft Defender Antivirus. If this policy setting is enabled, Microsoft Defender Antivirus does not run and computers are not scanned for malware or other potentially unwanted software.

When the setting is disabled and a third-party antivirus solution is installed, the two applications can both simultaneously try to protect the system. The two AV solutions both attempt to quarantine the same threat and will fight for access to delete the file. Users will see conflicts and the system may lock up until the two solutions finish processing.

When the setting is not configured and a third-party antivirus solution is installed, both applications coexist on the system without conflicts. Defender Antivirus will automatically disable itself and will enable if the third-party solution stops functioning. When the setting is not configured and Defender Antivirus is the only AV solution, Defender AV will run (default state) and receive definition updates. An administrator account is needed to turn off the service. A standard user cannot disable the service.