microsoft defender smartscreen prevented an unrecognised app from starting

The only two states you can set SmartScreen to are 'warn and prevent' or 'warn'. Note: if you want to keep SmartScreen turned on but want it to be less invasive, you may set the policy to enabled instead and the setting to 'warn'. Double-click on the policy Configure Windows Defender SmartScreen.

Go to Computer Configuration > Administrative Templates > Windows Components > File Explorer.

Type gpedit.msc and select the result (it may be called Group Policy Editor or gpedit.msc).

Tap on the Windows-key to display the Start menu.

Here is how you turn it off on Windows 10: Windows 10 Pro or Enterprise for the first method as you need to use the Group Policy Editor for that. You can still turn it off but need a professional version of Windows 10, e.g. Microsoft removed the Control Panel option to manage SmartScreen in recent versions of Windows 10. Turn off SmartScreen in Pro editions using Group Policy Note that disabling it may reduce the protection of the PC I suggest you do so only if you run into issues caused by it and/or use software that adds similar security functionality to the operating system. SmartScreen is part of Windows 10 as well, and you may still disable the feature if you don't require it. If Windows 8 is already installed, it won't do you any good. This option is however only available if you select a custom installation. I already described one of the options in the article that mentioned that SmartScreen reports back to Microsoft.

There are two options to turn off Windows SmartScreen in Windows 8.

Microsoft defender smartscreen prevented an unrecognised app from starting