Unable to start Windows defender - error 577

I recently (my fault) suffered a major malware attack. I removed the installed programs and ran malwarebytes which removed a great deal more junk. I then went to run a windows defender scan and got the following message.

This App is turned off by Group Policy ..  to allow this app to run

contact administrator to enable the program via group policy.              NOTE   I am sole user & administrator 2yr old Dell desktop using 8.1

I went to computer management , selected Windows Defender Service and clicked start. The app tries to start showing a progress bar, but fails to do so and I get the following message.

Windows could not start Windows Defender Service on local computer

Error 577 windows cannot verify the digital signature for this file. A recent hardware or software change might have install a file that is signed incorrectly or damaged or that might be malicious software from an unknown source.

I ran malwarebytes again with no affect. Then I downloaded the free version of AVG security software and scanned the system with it. AVG removed more malware and is running and protecting my pc. But did not restore Windows Defender. It also appears that windows auto update is not working.

I have tried to restore back to prior to the malware event but pc fails to restore to that point the next point available would take my pc way too far back.

Note my PC is currently preforming correct with no other issues or problems.

Original Title: mhscott16

Moved from Windows


Question Info

Last updated February 1, 2019 Views 6,154 Applies to:


Welcome to Microsoft Community. I will certainly help you with the issue that you are facing with your computer. This usually occurs when there are some corruptions caused to the Windows files.

I would like to inform you that if you have installed any third-party anti-virus software, it will disable Windows defender as it is not advised to keep more than one anti-virus on the system. Hence I would suggest you to try the following methods.

Method 1: Uninstall anti-virus

If you want to activate Windows defender, I would recommend you to uninstall al the other anti-virus software completely and then try to activate Windows defender and check if it helps.

To uninstall the software, you may refer: Uninstall, change or repair a program

Important Note: Antivirus software can help protect your computer against viruses and other security threats. In most cases, you shouldn't disable your antivirus software. If you have to uninstall it , you should re-enable/install other softwareas soon as you're done. If you're connected to the Internet or a network while your antivirus software is disabled, your computer is vulnerable to attacks.

Method 2: Run the System File Checker tool (SFC.exe)

System File Checker is a utility in Windows that allows users to scan for corruptions in Windows system files and restore corrupted files. It will scan your system files and to repair missing or corrupted system files in Windows. To run the SFC scan, refer to the Microsoft article below.


Hope this information was helpful. Let us know the results once you have tried these methods.

Thank You

Sahil Bali

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