Fix: Windows Defender Error 577 | Service Fails to Start

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

windows defender disabled - turn on button

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

windows defender error 577

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 filed that was signed incorrectly or damaged, or that might be malicious software from an unknown source.

Sometimes, you may see a different error.

windows defender service started and then stopped

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: Windows Defender 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.

(Related article: Fix: Malwarebytes Disables Windows Defender or 3rd Party Anti-Virus)

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)
  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’s Windows Sysinternals site. Unzip and extract the tool to a permanent folder, say d:\tools
  2. Open an elevated or admin Command Prompt window.
  3. Type the following command, and press ENTER:
  4. d:\tools\psexec.exe -sid c:\windows\regedit.exe

    regedit.exe psexec start as local system account
    The above PsExec command-line starts the Registry Editor under LOCALSYSTEM account so that you can modify protected areas in the registry.

  5. In the Registry Editor window, go to the following key:
  6. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Defender
  7. Double-click DisableAntiVirus and sets its data to 0
  8. Double-click DisableAntiSpyware and sets its data to 0
  9. disableantivirus and disableantispyware values set to 0

  10. Go to the following policies branch:
  11. HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
  12. Delete the two values DisableAntiVirusDisableAntiSpyware if found in the above location.
  13. delete disableantivirus and disableantispyware values

  14. Exit the Registry Editor.
  15. Restart Windows and see if Windows Defender is able to start correctly.

Automate the above steps using REG file

You can automate the steps 4-8 above by importing the REG file in the Registry Editor (launched using PsExec tool). Download fix-defender-error-577.zip, unzip and extract the REG file to desktop. In the Registry Editor window, click the File menu, click Import… and select the file fix-defender-error-577.reg to apply it. Exit the Registry Editor and restart Windows.

About the author

Ramesh Srinivasan founded Winhelponline.com back in 2005. He is passionate about Microsoft technologies and has a vast experience in the ITeS industry — delivering support for Microsoft's consumer products. He has been a Microsoft MVP [2003 to 2012] who contributes to various Windows support forums.

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