Windows 8.1: You cannot use Windows PowerShell to manage Windows Defender after installing the October 9, 2018 update

You install October 9, 2018—KB4462926 (Monthly Rollup) on a Windows 8.1-based computer. Then you open an elevated Windows PowerShell window to manage Windows Defender. However, you cannot import the Windows Defender module. When you run the Import-Module Defender command, you see a message that resembles the following:

Import-Module : The module to process 'MSFT_MpWDOScan.cdxml', listed in field 'NestedModules' of module manifest 'C:\windows\system32\windowsPowerShell\v1.0\Modules\defender\defender.psd1' was not processed because no valid module was found in any module directory.
At line:1 char:1
+ Import-Module defender
+~~~~~~~~~~~~~~~~~~~~~~~
   + CategoryInfo          : ResourceUnavailable: (defender:String) [Import-Module], PSInvalidOperationException
   + FullyQualifiedErrorID : Modules_ModuleFileNotFound.Microsoft.PowerShell.Commands.ImportModuleCommand

You cannot use PowerShell to manage Windows Defender on the affected computer. However, you can use WMI and Group Policy to manage Windows Defender on that computer.

On computers that run Windows 8.1 and have the October 9, 2018 update installed, the Defender.psd1 file contains a reference to MSFT_MpWDOScan.cdxml. However, this file does not exist on the affected computers. Because this file is missing, PowerShell cannot import the Defender module.

To resolve this issue, use one of the following methods.

• Use a text editor to modify the Defender.psd1 file. Remove all references to the following:
  • MSFT_MpWDOScan.dcxml
  • Start-MpWDOScan
• Replace the missing MSFT_MpWDOScan.cdxml file. To do this, follow these steps:

1. Copy the MSFT_MpWDOScan.cdxml file from a Windows 10-based computer or a Windows 8.1-based computer that does not have this update installed.
2. Paste the file into the C:\Windows\System32\WindowsPowerShell\v1.0\Modules\Defender\ folder on the affected computer.

   Note

   This step requires administrative permissions.

3. Open an elevated Windows PowerShell window, and run the following command:

   Import-Module Defender -force

   This command forces PowerShell to import the Defender module.