SOLVED: Windows Defender not starting after December ’14 Update

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Update: Microsoft has confirmed that this patch is flawed, and has issued another fix to automatically uninstall KB3004394. Even more fascinating, our experience that this “Windows Defender” update somehow impacted display adapters and video drivers has been confirmed. Continue to read our original post below.

Just the other day, I had the chance to experience this one hands on. We had a computer that would report that Windows Defender could not start automatically, shortly after the computer had rebooted from recent Windows Updates. Windows Defender in Windows 7 is important because it acts as an anti-malware solution, not just an antivirus. So even if you have something like AVG, Symantec, or even Microsoft Security Essentials, Windows Defender should be allowed to run in the background.

If you’re tech savvy, you may have even tried to go in to the Windows Services menu and attempted to start Windows Defender manually. If you try this, you will receive an error stating that “The Stub received bad data.” It turns out, there was a flaw in KB3004394, so simply uninstalling that for now will resolve the issue. I will provide the steps for uninstalling that patch.

Note: after uninstalling this patch, Windows Update will detect a “new” update, and offer KB3004394 for download again. There has been no word from Microsoft yet that this issue has been fixed. Our advice, for now, is to simply ignore this update. I do not advise hiding the update, because you want to be able to apply it when the proper fix arrives, but as of right now, others are still reporting the same issues.

  1. Click the Start Menu in the lower left.
  2. Type Programs and Features
  3. Press Enter
  4. On the left, click View Installed Updates
    • This full list can take a few minutes to populate.
  5. You may want to scroll to the right and ensure the “Installed on” column is how you are sorting this list.
  6. Under Microsoft Windows, find “Update for Microsoft Windows (KB3004394).”
  7. Either Double Click it to begin the uninstall, or click it once, then click the “Uninstall” button at the top.

It may take a few minutes to complete this process, but once it is finished, say “yes” to the reboot and when your computer comes back, it should be error free (hopefully you don’t have the display adapter issue we ran in to). Again, Windows Update will likely want you to reinstall the patch soon, but for the immediate future, it is safe to ignore it.