Please update to the latest threat definition version (1.239.1022.0 or higher) via Windows Update or the Windows Defender Client UI. If you are still experiencing the same 0x80070643 behavior, we recommend doing one final manual update with the latest packages from the adl portal: https://www.microsoft.com/security/portal/definitions/adl.aspx. From the portal please download and install both ‘Antimalware and antispyware updates’ and ‘Network Inspection System updates’ that works for your system.
I just wanted to start a thread to have a chance to address everyone and inform you that the Windows Defender team is aware of the situation and working as quickly as possible to resolve the issue. We thank you for your patience and we should have a fix rolled out soon.
Meanwhile, for those running into the definition update error 0x80070643 (or protection definition error: -2147023293) we recommend you to manually get your machines back to a protected state by following the instructions outlined here: https://www.microsoft.com/security/portal/definitions/adl.aspx.
Please note the manual adl package is designed to update silently. To verify the manual update worked correctly please check with the Windows Defender (or SCEP) Client UI to see if it reports the latest threat definition version. The latest definition version can also be found in the link above (currently 1.239.797.0).