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Windows Defender has been unable to install definition updates.  Is there a log file somewhere that I can check to try to figure out what is causing the problem?



You can use the MpCmdRun.exe tool to enable definition updates diagnostics.

  • Click the Start button, type cmd in the search box, right-click cmd in the Programs list, and then click Run as administrator.
  • At the command prompt, type the following commands. Press ENTER after each command:

cd C:\Program Files\Windows Defender


MpCmdRun -SignatureUpdate -Trace -Grouping 15 -GetFiles


  • At the command prompt, type exit, and then press ENTER to close the command prompt.
  • When the tracing is complete, examine the Mptrace.log file. The file is located in the following folder:

C:\ProgramData\Microsoft\Windows Defender\Support\Mptrace.log 

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