Windows Defender Error Code 80004002

Find the Definitions
Go to the Microsoft Security Portal website and follow the instructions to download the most recent definitions. After the file downloads, double-click it to install the definitions.
Check Your Computer
Restart your computer and check to see if you still get the same error message. If you do, go to Microsoft's Windows update page to determine whether you have the most current version of Windows. If you do not, this could have caused the error.
Contact Customer Support
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Windows Defender sometimes encounters problems downloading the most recent virus definitions.
If neither of these options work, contact Microsoft Customer Support. The problem likely involves some advanced troubleshooting that inexperienced computer users should not try without help.