Several users of Windows 10 are reporting that Windows Defender updates are failing to install and they receive a message:
Windows failed to install the following update with error 0x80070643
Windows Defender is failing to install updates
One user reported that the issue started for him after Cumulative Update for Windows 10 Version 1703 for x64-based Systems (KB4016250) was installed.
Another aggrieved user said:
This problem is not just limited to Insider builds I should add. I have checked several computers and the error occurs even on version 1607, which is the version on consumer computers! How many non tech users are now being left vulnerable because of this mess up. Also how many will do manual updates?
@PaulStreeting tweeted to us:
I have tested this bug on v1607 and does not apply only to ‘Insiders’ but the one pushed to users now..what is worrying is that the problem happens on v1607…so how many users are doing the manual update? Even after that it shows as error.
Microsoft has confirmed that they are aware of this issue and will roll out a fix soon:
Thank you for your patience regarding Windows Defender update error 0x80070643. We are aware of the issue and trying to roll out a mitigation as soon as possible. Meanwhile, to get your machine back to a protected state, you can manually download and apply the latest Definition Update.
Check if your Windows Defender is updating automatically
I strongly urge you to check if your Windows Defender is updating automatically. If not, you should download and install the Windows Defender updates manually.
Open Windows Defender > Update > Update definitions. Or else, go to Settings > Update & Security > Windows Update > Check for updates. See if you can update it automatically.
If you cannot and if you are facing this issue, it is recommended that you update Windows Defender manually periodically till the problem is fixed by Microsoft.
If you don’t want to get into the mess of checking up for updates, downloading them and applying them, I suggest that you use a third-party freeware antivirus software till Microsoft fixes the issue.
If you wish to troubleshoot the issue futher, perhaps this post will help you – Windows Defender will not update definitions.