Windows defender definition update bugged?

A Spicy Noodle · Jan 23, 2018

When I press check for updates it doesn’t show any results just the bar then returns back to normal and allows me to press check for updates again. Sometimes it’ll give an error and say protection definition update failed. Can someone help me solve this?

das_stig · Jan 23, 2018

Open command prompt as admin and try ..

cd %ProgramFiles%\Windows Defender
MpCmdRun.exe -removedefinitions -dynamicsignatures
MpCmdRun.exe -SignatureUpdate

If that doesn't work, try the offline definition installer.

https://www.microsoft.com/en-us/wdsi/definitions

A Spicy Noodle · Jan 23, 2018

das_stig :

What does this command do and I am using windows 10 if that matters.

rgd1101 · Jan 23, 2018

MERGED QUESTION
Question from A Spicy Noodle : "Windows Defender protection definition update failed"

A Spicy Noodle :

I started my PC it was very slow. I checked the task manager I saw that Antimalware Service Executable was taking up a lot of the CPU and Disk %. I restarted my PC and then turned it back on. It was still very slow, I became worried that I might have interrupted a update for windows defender so I tried to check for updates. when I click check for updates it tells me protection definition update failed. I followed this thread telling me to start command prompt and run it as admin then type DISM.exe /Online /Cleanup-image /Restorehealth after that I typed sfc /scannow. It didn't work in normal mode so I started in safe mode because the thread said so. It worked in safe mode and said that no files were corrupted. My PC is much faster now but windows defender still doesn't check for updates and gives me Protection Definition Update failed. I have read something on manually install the updates. Should I try that out then check for updates again? and if so how should I go about manually installing the updates. thank you very much for taking your time to read this and hopefully help me.

A Spicy Noodle · Jan 24, 2018

das_stig :

also what do I not type into the command prompt do I type cd and MpCmdRun.exe?

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