Quite recently I saw a notification to update to the latest version of Microsoft Security Essentials, however, the update kept failing because of a "0×80070643" Error. This issue kept happening multiple times and I did find a solution for it. So how do you fix the 0×80070643 Error that occurs while installing or updating Microsoft Security Essentials? Read ahead.
There are various reasons why this error may occur, it could vary based on whether you are installing or updating MSE, I will categorize the problems and their solutions.
Microsoft Security Essentials 0×80070643 Install/Upgrade Errors
Cause 1: You might have another Antivirus programs installed while you are installing MSE.
Solution 1: Uninstall all the other Antivirus programs before installing MSE and try again, this should resolve the 0×80070643 error.
Cause 2: You might be not be using an older version of Windows Installer
Solution 2: Upgrade windows or download the latest version of Windows Installer. MSE requires at-least version 3.1 of Windows Installer or higher.
Cause 3: Windows Installer service is turned off.
Solution 3: Go to Start -> Run and type in "services.msc", scroll down till you find the Windows Installer service and start it. You might want to change the startup type to automatic. If you aren’t sure how to deal with services, you might want to read up a similar post on starting a Windows service and turning it on automatically.
There may be several other causes why this happens. I will try and update this post once I get to more scenarios and add solutions to it.