Windows 11 and 10 Defender Security won't open.

Windows 10 and Windows 11 have a built-in (and pretty good) Microsoft Defender Antivirus (Windows Defender), managed through the Windows Security panel. In some cases, Windows Defender or the Windows Security control panel stop opening, an empty white window is shown instead of a dialog interface, the application does not start when called through the Settings panel or the shortcut command ms-settings:windowsdefender . In this article, we will look at how to fix common errors when the Windows Defender Security Service window cannot be opened.

First of all, check if a third-party antivirus is installed in Windows. Windows Defender in the Windows Security Panel is automatically disabled when using non-Microsoft antivirus. Decide which antivirus you want to use in the future, if you need to leave Windows Defender, remove the third-party antivirus.

If when you start Windows Security (Windows Defender) through the Settings menu (Settings -> Update & Security -> Windows Security), a window appears prompting you to select programs to open the “ You’ll need a new app to open this Windowsdefender link ” link, check that the Microsoft.SecHealthU UWP application is installed. It is the UWP Windows Security app (Windows Defender) that is responsible for displaying the Windows Security window.

Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage

Make sure all Microsoft Defender services are running on Windows. The following services must be running on Windows:

• Microsoft Defender Antivirus Service (WinDefend)
• Windows Security Service (SecurityHealthService)
• Security Center (wscsvc)

You can check the list of running Windows Defender services through the services.msc control panel or using PowerShell:

get-service WinDefend, SecurityHealthService, wscsvc | select name,status,starttype

If the services are disabled, change the startup type to Automatic and restart the computer.

The Windows Defender Firewall (mpssvc), Microsoft Defender Antivirus Network Inspection Service (WdNisSvc), and Windows Defender Advanced Threat Protection Service (Sense) services are optional for the Security Control Panel to work.

In the Windows Security Control Panel, the message “The Threat Service has stopped, please restart it ” may hang. To fix this Defender error, follow this guide.

On Windows 10 and 11, Microsoft Defender is automatically turned off if a third-party antivirus is installed on the device. If there is no third-party antivirus, and Microsoft Defender is disabled, then someone tried very hard to disable it.

To completely disable Microsoft Defender in Windows 11, you need to disable Windows Defender services in safe mode through the registry and edit permissions on registry branches.

Starting with Windows 10 2004 (including Windows 11) you cannot simply disable Microsoft Defender with:

• registry keys DisableAntiVirus=1 and DisableAntiSpyware=1 ( HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender);
  
• or the Turn off Microsoft Defender Antivirus GPO setting in Computer Configuration -> Administrative Templates -> Windows Components -> Microsoft Defender Antivirus.

To disable Windows Defender, you first need to disable the Microsoft Defender Tamper Protection feature in Microsoft Defender settings.

You can check if Defender antivirus protection is disabled using PowerShell :

Get-MpComputerStatus | select IsTamperProtected

In this example IsTamperProtected=True , this means that Windows Security is blocking Microsoft Defender from being turned off.

In earlier versions of Windows 10, check the value of the above local group policy setting using the gpedit.msc editor (the setting must be set to Not configured or Disabled ) or using PowerShell:

Get-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender' -Name DisableAntiSpyware
Get-ItemProperty -Path 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender' -Name DisableAntiVirus

If the command returns parameter value =1, then Microsot Defender is disabled. To enable Windows Defender, remove the setting or change the value to 0.

Check and install the latest Windows Settings -> Update & Security -> Windows Update -> Check for updates or using PowerShell.

If all else fails, check and fix the integrity of the Windows image with the commands:

sfc /scannow

and

DISM /Online /Cleanup-Image /RestoreHealth

The instructions in this article should restore the Windows Security service.