Windows 10: WIndows Defender Definition Update Failure Solved

  1.    12 Dec 2017 #1

    WIndows Defender Definition Update Failure

    I'm getting a failure updating Windows Defender Antivirus definition (error 0x800070643, protection definitions update failing with error code -2147023293, "fatal error during installation") through Windows Update and by updating within the protection updates function of Windows Defender. The definitions are stuck at, but the installation seems to fail right at the end of the installation process. Windows 10 itself is fully updating. This is a new Microsoft Surface Pro (2017) and the definitions had been updating properly. Any thoughts would be appreciated.

    (I've tried all of the Windows Update troubleshooting tools, and everything I've found on the Internet is either old, does not apply, or does not work.)
      My ComputerSystem Spec

  2. Posts : 693
    Windows 10 Pro 64bit 1809 17763.55
       12 Dec 2017 #2

    Same issue here with Defender Definition updates, every other update finished properly, just not sure why this one didn't for some reason, and Just Switched over to Defender myself yesterday, after using Avast for 14 years on various Computer systems, but if this issue remains I can always switch back to Avast for security if need be
      My ComputersSystem Spec

  3.    12 Dec 2017 #3

    Definition update to also failed, although it too a lot longer during the attempted installation to run before it failed. Each of my other machined is successfully updating the definitions. Sigh...
      My ComputerSystem Spec

  4.    12 Dec 2017 #4

    An update: This problem is being reports elsewhere too. The device is receiving a signature that is invalid, and the update is blocked. Microsoft apparently has a fix deployed in Windows Update. Version 1.259.227 definitions seems to install properly. Now why did I do all that troubleshooting, including resetting my brand new Surface Pro that I has just about gotten customized fully? Microsoft....grrrrrrrrr.....
      My ComputerSystem Spec

  5. Posts : 693
    Windows 10 Pro 64bit 1809 17763.55
       12 Dec 2017 #5

    Update: 1.259.227 finally installed right, thankfully I didn't stop using it and switch back to Avast like I almost did, decided to check one more time, and that time it finally seemed to update right about time
      My ComputersSystem Spec

  6.    12 Dec 2017 #6

    Defender working different since the update or the Windows update update, not sure which caused it. I had a daily manual Quick scan scheduled and had disabled periodic scans. I think I must have reenabled the Health scans but my scheduled scan has not run since the Defender update. Also get the new style notification open when the Health scan completes. Need to look more in to it.
      My ComputerSystem Spec


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