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Reboot Clears Defender Error 0x80070643

As I performed my usual test systems check this morning, I encountered an error. On my Surface Pro 3, it appeared in Settings → Update & Security → Windows Update. In downloading an update to the Defender antimalware platform, error  0x80070643 got thrown. “Good,” I thought, “now I can download and try out the Microsoft Error Lookup Tool I read about last week.” As further research showed me, a simple reboot clears Defender error 0x80070643. That was easy, and gave me a chance to use a tool that rightfully belongs in my admin toolkit. Here’s what the initial error info looked like:

An important clue to solving this error appears as a blue “Retry” button at lower left.
[Click image for full-sized view.]

Learning That Reboot Clears Defender Error 0x80070643

Before I tried anything with that button, I zipped into Windows Security → Virus & threat protection. There, I was informed that the Threat service had stopped and needed to be restarted. (This is just as one might expect, when updating the antimalware platform. Stopping the threat service would be a necessary preamble.)

I pushed the button, but nothing happened. Hence, the reboot.

After pushing the “Restart now” button shown above, the progress balls kept rolling, and the restart process failed. I could only conclude that antimalware installation had gotten underway, but didn’t complete successfully. My presumption: no working code to run the threat service means no start-up is possible. Because something was stuck, long experience told me “This is something a reboot might mix.” It did!

The Error Lookup Tool Sheds Additional Light

When I ran my brand-new lookup tool at the command line, it provided additional insight. (Note: the program is named err_6.4.5.exe, as shown in the following PowerShell window. It takes the error code as an input argument.) Here’s what it told me:

This item decodes as “Fatal error during installation.” No wonder the Threat service wouldn’t start!
[Click image for full-sized view.]

Thus, my initial diagnosis that the antimalware engine went completely south was confirmed. Following a fatal installation error, a retry is the only way to restore those code elements to proper operation. After a reboot, Windows Update did the job automatically and admirably. Problem solved.

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