Error code 0x8000404 is one of the most frequent errors encountered by Windows Defender users, and appears when the definition updates can’t be installed. There are several possible causes for this error: another security program creates conflicts and blocks Windows Defender updates, some system files are corrupt or missing, the Internet connection in unstable, and more.

Fix Windows Defender error 0x8000404

Fix – Error 0x8000404 in Windows Defender

Solution 1 – Disable third-party antivirus

As we already know that Windows Defender is a part of the system, so installing a third-party antivirus can lead to certain interferences. In that manner, it’s advisable to disable a third-party antivirus in order to make Windows Defender work again. However, you might consider changing your antivirus for a more efficient solution, so we recommend picking the best antivirus tools with high detection rates.

Solution 2 – Make sure the Windows Defender service is running

For Windows Defender to run properly, you need its service to run properly. Obviously, if the service doesn’t work, neither will Windows Defender. In that manner, let’s go and check if the Windows Defender service runs properly, and re-enable it if not. Here’s how to do that:

Solution 3 – Make sure Windows Defender is running

Even if the service is running properly, the firewall itself could be disabled. Now, it should be enabled by default, but let’s check just in case. Here’s how to do that:

Solution 4 – Check for updates

As Windows Defender is part of the system, Microsoft releases updates for it through Windows Update. So, if there’s something broken inside Windows Defender, go on and check for updates. Maybe Microsoft has an ‘automatic’ solution. To check for updates, simply go to Settings > Updates & Security, and check for updates. SPONSORED

Solution 5 – Remove latest updates

Just like installing a simple update can resolve the whole problem, it can also cause it in the first place. It’s actually a common sight that some cumulative update actually breaks something inside the system, and it could easily be Windows Defender. So, if you suspect the latest update you installed could have caused the problem, go on and delete that update. If you’re not sure how to delete updates in Windows 10, just follow these instructions:

Solution 6 – Run the SFC scan

The SFC scan is a universal troubleshooting tool that can be used for fixing all sorts of issues in Windows 10. So, it might be helpful in this case, as well. Follow these steps to run the SFC scan in Windows 10:

Solution 7 – Check the environment variables

Environment variables are a useful feature used by your system to access certain directories. However, sometimes users or perhaps a third-party application can change the environment variables and cause issues with Windows Defender. To fix your environment variables manually do the following: That’s about it. If you’ve come across other workarounds to fix Windows Defender error 0x8000404, list the troubleshooting steps in the comment section below.

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