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Published on 03.06.08 by Brent Trahan

Roll Back the Signature Definitions in Windows Defender

Learn how to roll back or uninstall the signature definitions and engine files for Windows Defender.

If you’re having a problem updating Windows Defender’s definitions try rolling back the definitions to the last set or completely uninstall all signature definitions and engine files.

Roll Back the Signature Definitions

  1. Click the Start orb, All Programs, Accessories, and then right-click Command Prompt and select Run as Administrator to start an elevated command prompt.
  2. Type C:\Program Files\Windows Defender\MpCmdRun.exe –RemoveDefinitions in the command prompt.
  3. Press Enter on your keyboard.

Windows Defender’s signature definitions will be rolled back to last set. You can try re-downloading the latest signature definitions.

Uninstall All Signature Definitions and Engine Updates

  1. Click the Start orb, All Programs, Accessories, and then right-click Command Prompt and select Run as Administrator to start an elevated command prompt.
  2. Type C:\Program Files\Windows Defender\MpCmdRun.exe –RemoveDefinitions –All in the command prompt.
  3. Press Enter on your keyboard.

Windows Defender’s default signature definitions and engine will be loaded. You can re-download new signature definitions and engine updates now.

Still need help? Ask your computer question now.

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3 Responses to “Roll Back the Signature Definitions in Windows Defender”

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  1. ak says:

    hye….
    tried…
    but it said…
    command not recognize….
    so can you tell me wat to do?

  2. Mark says:

    Thanks for publishing this tip! I just had a routine Windows Defender update fail for no apparent reason, with an error code not covered by Microsoft’s help. Windows Update wouldn’t offer me the opportunity to try re-downloading and re-installing the failed update (because it was already there in my update history), and there was no way provided to uninstall the failed definition and try again.

    I uninstalled all of the signature definitions and solicited updates from Windows Update again. The failed update succeeded this time.

    *thumbs up* :-)

  3. Dora says:

    Never would have thunk I would find this so indspienasble.

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