When a Windows user upgrades their computer from Windows 7, 8, or 8.1 to Windows 10, the Microsoft Security Essentials (MSE) program, 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 assume all duties and responsibilities of Microsoft Security Essentials.
However, in some cases, when a Windows user upgrades from a previous version 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 might not see this as a problem, but it is actually a significant issue. This is because MSE, which was not designed to work with Windows 10, doesn’t function on the recently upgraded computer. Moreover, since Windows Defender did not successfully replace MSE, it also fails to work. Therefore, every time the user opens the computer, they receive a popup message from Windows Defender stating that it is disabled.
The problem further intensifies when the user attempts to uninstall MSE to enable Windows Defender to function, but fails. Instead, they receive an error message stating that MSE cannot be installed, regardless of the method they use to try and uninstall MSE. This problem stems from the way Windows Defender was programmed. It was designed to inhibit the installation of MSE, but it unintentionally also obstructs the uninstallation of MSE. As a result, uninstalling Microsoft Security Essentials on Windows 10 becomes slightly more complex. However, by following the subsequent steps, you should still be able to successfully remove Microsoft Security Essentials from a Windows 10 computer.
Press the 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. 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.