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Fix: Windows Defender Error 577 | Service Fails to Start

The “Security and Maintenance” Control Panel applet or the Action Center in Windows 10 may warn you that Windows Defender is disabled and no anti-virus is protecting your system. If you open the Windows Defender interface, it offers to Turn On protection, but the button doesn’t work.

In the Services MMC, when you try to start Windows Defender Antivirus Service (now “Microsoft Defender Antivirus Service”) or Windows Defender Antivirus Network Inspection Service (“Microsoft Defender Antivirus Network Inspection Service”), you may get Error 577, as seen below:

Windows could not start Windows Defender.

Error 577: Windows cannot verify the digital signature for this file. A recent hardware or software change might have installed a file that was signed incorrectly or damaged, or that might be malicious software from an unknown source.

Sometimes, you may see a different error.

The Windows Defender Antivirus Service service on Local Computer started and then stopped. Some services stop automatically if they are not in use by other services or programs.

Fix: Microsoft Defender Antivirus Service Error 577

This problem can happen if you’ve been using a 3rd party anti-virus solution and later uninstalled it or its trial period has ended. Installation of a third-party anti-virus program automatically disables Windows Defender anti-virus.

If a trial version of your anti-virus software (i.e. Avast, McAfee, Norton, etc) came preinstalled on your computer (or you installed one), it most likely turned Windows Defender off to avoid conflicts.

Until the third-party anti-virus software has been completely uninstalled, Windows Defender will remain disabled. Sometimes, you’ll need to download and run the anti-virus software vendor’s uninstaller/cleanup tool to remove traces of the software completely. Once done, Windows Defender and the related services should resume automatically.

Step 1: Uninstall third-party anti-virus software

Open Apps & Features or Programs and Features and uninstall the third-party software. If the uninstall process fails, or the uninstall doesn’t fix the problem even after restarting the system, use the specialized cleanup tool from the respective anti-virus software vendor.

  1. Avast Uninstall Utility (aswClear)
  2. AVG Remover
  3. Avira: Manual uninstallation instructions
  4. Bitdefender Uninstall Tools
  5. Removal tool for Kaspersky products (kavremover) – Direct download kavremvr.exe
  6. F-Secure Uninstall Tool
  7. Remove McAfee products
  8. Uninstall ESET manually using the ESET uninstaller tool

Also, see the comprehensive list of anti-virus uninstaller tools compiled by ESET Knowledgebase team: Uninstallers (removal tools) for common Windows antivirus software.

Step 2: Fix Windows Defender Registry Settings

If clean uninstalling third-party anti-virus solution and restarting Windows doesn’t help, follow these steps in addition:

  1. Download PsExec from Microsoft Sysinternals.
  2. Unzip and extract the tool to a permanent folder —  e.g., d:\tools.
  3. Open an elevated or admin Command Prompt window.
  4. Type the following command, and press ENTER:
    d:\tools\psexec.exe -sid c:\windows\regedit.exe

    The above PsExec command-line starts the Registry Editor under LOCALSYSTEM account so that you can modify some protected keys in the registry.

  5. In the Registry Editor window, go to the following key:
    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Defender
  6. Double-click DisableAntiVirus and sets its data to 0
  7. Double-click DisableAntiSpyware and sets its data to 0
  8. Go to the following policies branch:
    HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
  9. Delete the two values DisableAntiVirusDisableAntiSpyware if found in the above location.
  10. Exit the Registry Editor.
  11. Restart Windows and see if Windows Defender is able to start correctly.

Automate the above steps using a Registry file

You can automate the steps 4-8 above by importing the .reg file in the Registry Editor (launched using PsExec tool).

  1. Download, unzip, and extract the .reg file to the desktop.
  2. In the Registry Editor, click the File menu, click Import…
  3. Select the file fix-defender-error-577.reg to apply it.
  4. Exit the Registry Editor.
  5. Restart Windows.

Hope the above steps have resolved the Microsoft Defender Antivirus Service error 577.

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