While trying to update Microsoft Security Essentials to the newly released version 2, the installation failed with the remarkably descriptive error 0x80070643. Looking for a solution on the web was no help either.

So I tried to solve the problem by uninstalling the old version. Installing all critical and optional updates via Windows Update. Rebooting multiple times while doing so. Deactivating Microsoft Defender's real-time protection. Sacrificing two goats and finally handing over my soul to the devil.
But nothing worked.

At the end I got it to work. However, I changed two things at once before trying to install MSE2 again, so I'm not sure which one of those changes actually fixed the problem.
But here you go:

  • STOP the "Windows Defender"-service (I don't think that solved the problem)
  • START the "Windows Firewall"-service (But this one did, I guess)

As I don't use Microsoft Firewall (or any other firewall software), I didn't just deactivate the firewall but stopped the service altogether. That seems to have bothered the installer.

Now MSE2 is installed and working properly and with that: the option to opt-out of SpyNet.

02011-Jan-26, Wed 14:53
Oh, man, you are GOD!!! I've spent all day destructing my brain and my PC, but nothing worked. Your discovery is great! Thank you so much, I would never guessed it myself.
02012-Jun-14, Thu 5:52
don't work=(
02013-Jun-5, Wed 6:31
Saiful Alam
Install KB893803 V2 then try. Tested.
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