How to FIX Windows update error 8050800C about Windows Defender Definition Update

Did you receive the 8050800C error from Windows update while trying to get the Windows Defender updates? I did with my Windows 7 Pro 64.  Lots of sites tell a lot of stupid things to try, things that are only there to make the site catch more Google hits to serve more ads. Nobody seems to test their stuff anymore. I did. And I have a working, tested solution.

Executive summary of fix:

  1. Download the the Windows Defender update file manually (mpas-fe.exe, available from https://www.microsoft.com/en-us/wdsi/definitions )
  2. Start Windows in safe mode
  3. Run the downloaded exe in safe mode and reboot (or optionally run the exe with Windows Update Service disabled)
  4. It’s fixed!

For more details and illustrated guide, read more below.

The Problem: Windows Update error code  8050800C while trying to download Windows Defender definitions

Have you perhaps installed your trusty old Windows 7 from scratch and you are finishing on the whole Windows Update ordeal? This was the case for me. I had installed Windows 7 Pro 64 UK on a used computer I recently bought cheaply. I constantly used method called disk images while installing. Whenever I successfully completed a phase (installing drivers, activating windows, making a set of updates) I launched my SystemRescueCD and saved the Windows installation as disk images.

Whenever I started getting errors for example in the Windows Update for wrong update order (yes, order matters for some sad reason…), I just reverted back to earlier disk images. Things were good until I was down to this last update:

So I tried to install it. What happened:

Failure. I tried many times in a row, always failure:

The problematic update in my case (as of 2019-04-09 ) was called “Definition Update for Windows Defender Antivirus – KB915597 (Definition 1.291.1464.0)” and it never got installed. I searched for a bunch of sites with Google but they did not provide solution. They just cooked some shit up to get advertisement revenue without helping users.

I started to experiment myself. After many tries later I was finally able to deduce a solution that works all the time. At least for now. There is no guarantee that the case remains the same later. But hopefully I can actually help some people with this.

The Solution

Go to Google first, Google for: windows defender definitions download. Like this:

First result is probably from Microsoft:

Follow the link, which is currently https://www.microsoft.com/en-us/wdsi/definitions

Scroll down to your operating system and bits version.  Mine was Windows 7 64-bit:

So click on the correct link to begin downloading the file:

The file is called mpas-fe.exe (at least today) and it is over 50MB in size. Save the file to desktop:

OK, to make things simple we need to next go to Windows Safe Mode. How? First click on the restart button:

Now watch the machine to restart. But keep hitting F8 continuously as the machine boots:

Now this menu appears. Select Safe Mode:

Ok now you get into Safe Mode. Then in the desktop look at the file mpas-fe.exe , right click on it and select Properties:

Check that the file is as expected. For me the file name was indeed mpas-fe.exe and size was over 50MB. I checked also the Details page of the file info and it showed the file version to be 1.291.1457.0 today. Of course it may change in the future.

Ok, now press OK to close the file info. Then double-click on the mpas-fe.exe . You may get the following warning:

You can press Run. It may now look like that nothing is happening, but trust me, the exe file is actually working in the background:

Next, restart the computer to exit Safe Mode:

Ok now Windows starts again. For me magic started to happen now. I ran “Check for updates” from Windows Update and it showed this:

So the offending update had actually changed! What I was now offered was “Definition Update for Windows Defender Antivirus – KB915597 (Definition 1.291.1464.0)”:

So the same as earlier? No. Take a look at the file size. It was now down to few megabytes.

Installing the update worked:

After this install I got offered 2019-03 Servicing Stack Update:

Of course I again at this point remind that in the future (past 2019-04-09) you might get offered something else. Anyways, the update succeeded:

And… Windows Update offered no more updates!

So I consider issue resolved!

Afterthoughts

I did a bit more testing during writing this post and it looks like one can get the mpas-fe.exe installed in normal mode if one temporarily disables the Windows Update service. But I think it is more easier and more solid way to go directly to Safe Mode for install.

23 thoughts on “How to FIX Windows update error 8050800C about Windows Defender Definition Update”

  1. Thank you for your solution. You might consider mentioning the option to disable Windows Update service instead of safe mode in your short directions. Example:

    Download the the Windows Defender update file manually (mpas-fe.exe, available from https://www.microsoft.com/en-us/wdsi/definitions )
    Start Windows in safe mode OR disable Windows Update Service
    Run the downloaded exe in safe mode and reboot OR with Windows Update service disabled and no reboot
    It’s fixed!

    1. Thanks for posting this. You saved me some time getting a clean Windows 7 virtual environment up and running.

      FYI, I didn’t need to use Safe Mode or disable the Windows Update service to get mpas-fe.exe to run successfully and resolve the Windows Update failures. It ran without issue, I confirmed the definitions had been updated via Event Viewer (Applications and Services Logs > Microsoft > Windows > Windows Defender > Operational), and Windows Update started working. Happy days!

  2. Thank you for your well done research to resolve this error. I followed your advise and updated my system successfully.

  3. Thanks Janne!
    I used the method of stopping the Windows Update service from the ‘Services’ followed by running the exe update file.

  4. GOD BLESS YOU!!!!!Ahhhhhhh!!!! I can stop pulling my hair out now! Almost same situation with me where I wiped everything and did a clean install. Then came the tedious updating of windows software. Got stuck on this one and same as you, found annoying “answers” that got me no where. Anyways, Thank you so much!

  5. Hello Janne,
    Preface: I just did a 3-day Windows 7 Ultimate install from scratch for a Virtual Machine for regression/compatibility testing. 1 hour to install, the rest to upgrade. I’ve got 3 more to make. Yay.

    Anyhow, I’ve been banging my head trying to resolve this issue for the past 5 hours. After trying everything I know and getting nowhere, then doing the Google search thing like you, and finding a lot of nothing on click-bait sites, I landed here.

    All I have to say is, thank you very deeply from the bottom of my heart. Your solution worked flawlessly. You saved a life…my computers. I was about to turn it into a Shot put. Yes, I know, a bit of misplaced aggression. =)

    It must’ve taken you quite a while to compose this post, along with the helpful screenshots.

    Once again, thank you! You saved my sanity.

    -Trystian
    (Former M$ SDET/Developer)

    1. I forgot to include the offending Update info…

      Security Intelligence Update for Windows Defender Antivirus – KB915597 (Version 1.317.247.0)
      Installation date: ‎5/‎30/‎2020 1:57 PM
      Installation status: Failed
      Error details: Code 8050800C

    2. Glad to hear from you, Trystian! Yeah, the amount of click-bait sites about the issue is enormous. They just copy each other and nobody tests it and nothing works anymore. Crazy.

      I spend enormous amounts of time with each blog post normally. Because I have learned at work that it needs to be done in pictures so that everyone understands. I have worked with a lot of different nationalities and especially those lacking passable knowledge of English (I’m a Finn). Not their fault, it just happens. But yeah, I developed this habit of putting detailed screenshots to everything I do. Every report, presentation and plan. It takes a lot of work but it is really heart-warming to hear all these comments every now and then from people who I have helped. It means a lot to me. Thanks!

  6. Some of you might find this interesting: I’m planning to make a dedicated blog post about patching Windows 7 via Windows Update. I recently needed to update slightly modified Windows 7 64 Pro UK SP1 from scratch and it was a nightmare with failing updates and ad-hoc crypto patches, etc. I used one virtual machine to babysit another about proper upgrade paths. And this is probably planet’s #1 consumer software…

  7. Thank you so much. Another person here setting up Windows 7 in June 2020. Great to have this workaround/fix.

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