The Malware message is the result of a setting and Apple has work around for their own limits The setting is in General System Preferences and it limits installers to those from the App Store. You can change this to allow from Identified Developers.This is a new policy that requires installers to obtain new notarization annually, even if there is no change.

Apple used to have an option to Allow from all developers, but they removed that. They still allow you to install from all developers, but make you jump through some hoops. Here is a link if it posts. It is Apples own support.

https://support.apple.com/en-us/HT202491

They apparently can block some applications installed from running if not Notarized, but also offer a solution for that currently.

Apple has indicated they want to move to only apps from the App Store, and as a business model, it makes sense, since they get paid for every application obtained through the App Store.

ratscloset
aka John