Windows Defender is the default antivirus solution for Windows 10 just like it has been on Windows 8. The program is enabled by default and will turn itself off if another antivirus solution is installed provided that it is recognized by the operating system.
One core difference between the implementation of Windows 8 and 10 is that you cannot turn off Windows Defender completely anymore using the preferences provided in the application.
A click on Settings in Windows Defender opens the control panel for the program in the new Windows Settings application. While you find options to toggle the program's real-time protection there, it is indicated right on the page that this is just a temporary state change.
You can turn this off temporarily, but if it's off for a while we'll turn it back on automatically.
It is unclear why Microsoft made the decision to change the behavior of Windows Defender in this regard. What is certain however is that it will annoy users who want to disable it permanently on the computer they are working on.
While you could go ahead and disable Windows Defender whenever it enables itself automatically again, you may prefer a solution that is permanent.
There are two options that you have to disable Windows Defender permanently on a system running Windows 10. Please note that one of the methods is only available in some versions of Windows.
Method 1: Disabling Windows Defender using the Group Policy
The Group Policy Editor is only part of Windows 10 Pro and Enterprise. To turn off Windows Defender using it do the following:
Tap on the Windows-key to open the Start Menu.
Type gpedit.msc and hit enter.
Confirm the UAC prompt to continue.
You find the setting by following this path: Local Computer Policy > Computer Configuration > Administrative Templates > Windows Components > Windows Defender.
There you find the policy "Turn off Windows Defender".
Double-click on the policy.
Set the state of the policy to enabled in the window that opens, and click ok to save the change.
The policy reads:
This policy setting turns off Windows Defender.
If you enable this policy setting, Windows Defender does not run, and computers are not scanned for malware or other potentially unwanted software.
If you disable or do not configure this policy setting, by default Windows Defender runs and computers are scanned for malware and other potentially unwanted software.
Windows Defender is disabled immediately when you make the change. Any attempt to run the program afterward results in the following error message.