You don't need to turn OFF this option in the Security Prefrences if you want to keep your Mac secure. For this just right-click, or ctrl-click the installer icon and select "Open" from the menu. This way of "Open" will display an extra button to simply allow the security exemption only once. This stops people from accidentally double clicking an malitious installer and that's a good thing. Those people that only kow how to double-click are not thinking ahead. Those that know the workaround seem to know what they are up for. By the right-click method a grandma or child confirms to the OS he or she knows something is going to be installed thereafter.
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