When a Windows user upgrades their computer from Windows 7, 8 or 8.1 to Windows 10, the Microsoft Security Essentials (MSE) program that is designed to act as the onboard security program for these versions of the Operating System is meant to be replaced by Windows Defender. Windows Defender is the resident security program for Windows 10 and is designed to take over all of Microsoft Security Essentials’ duties and responsibilities.
However, in some cases, when a Windows user upgrades from a previous version of Windows to Windows 10, something goes wrong and Windows Defender does not replace MSE. Instead, both MSE and Windows Defender start to exist on the same computer. Most people would not see this as a problem, but this is an extremely big problem because, since MSE was not designed to work on Windows 10, it doesn’t work on the newly upgraded computer, and because Windows Defender did not successfully replace MSE, it does not work either. Instead, whenever the user opens the computer up, they get a popup message from Windows Defender saying it is disabled.
The problem becomes further intensified when the user tries to uninstall MSE in order to allow Windows Defender to do its job but fails and gets an error message stating MSE cannot be INSTALLED instead regardless of what method they use to try and uninstall MSE. The root of this problem is the fact that Windows Defender was programmed to prohibit the installation of MSE, but in doing so was also programmed to prohibit the un-installation of MSE. This makes uninstalling Microsoft Security Essentials on Windows 10 a bit more complicated, but as long as you go through the following steps, you should be able to successfully get rid of Microsoft Security Essentials on a Windows 10 computer:
Press Windows Logo key + R. Type taskmgr into the Run dialog and click OK
Locate and right-click on the Windows Defender Service (WinDefend) in the Services tab and click on Stop. Once the Windows Defender Service has been stopped, it will no longer prohibit you from installing (or un-installing) MSE, and you should be able to uninstall the program as though it were any other application.
Go to Control Panel > Programs & Features > Uninstall a Program.
Look for Microsoft Security Essentials in the list and uninstall It should now uninstall successfully.
Restart your computer.
Once your computer boots up, make sure that Microsoft Security Essentials was indeed uninstalled and that the Windows Defender Service (WinDefend) is up and running again in Task Manager > Services.