Windows Defender Update failing
In the last two weeks I have been getting this error
Windows failed to install the following update with error 0x80070643: Definition Update for Windows Defender
I'm getting the other updates, just Defender is failing.
Note for visiting users: The solution below contains some technical terms and some advanced methods for a new user. Please proceed with the solution only when you fully understand it. It can harm your PC. If you don't understand the steps then ask, we will explain you!
Let me give it a try. C:\Windows\Temp contains MpCmdRun.log and MpSigStub.log files which can give us more knowledge about the error happening with Defender.
After watching your logs, I found I saw a similar case (though that was of Windows 8.1) and the problem was resolved by this:
Stop Windows Update service, clear C:\Windows\Temp and %UserProfile%\AppData\Local\Temp (and clear SoftwareDistribution folder also), restart Windows Update service and try updating Windows Defender again.
If we clear those two temp folders we will lose the logs, so first copy them somewhere else (MpCmdRun.log file is also in User's Temp) and then try it.
Please mark replies as helpful/answer if they are.