Situation: When installing Windows update, you may receive this error: 0x80070643
Resolution: 1. Manually update Windows Defender to fix update failures KB2267602 (Definition 1.213.6196.0) – Error 0x80070643
by using this command
“%programfiles%\windows defender\mpcmdrun.exe” -signatureupdate -http
2. Download and install Windows Update Assistant from Microsoft. This step by step video may help: