I'd strongly disagree with the claim that a Mac needs third party anti virus/malware protection.
Though Andy's question is valid, your earlier description, in another thread, of the way SWMBO "just clicks on things and installs them", is pretty much a textbook description of someone at high risk for malware infection.
Not on a Mac, with the
default settings it isn't.
OSX is different from Windows with its default security settings. Windows will (or did at least, haven't checked the defaults on Windows 10) allow a default user download a random exe and run it (though may make them click "yes, please, run the random exe").
OSX in the last few versions doesn't work like that. With the default settings it simply won't let a user run a random exe (or as they are on OSX .app). It will only run exes from developers who have obtained a certificate from Apple and signed their exe.
Users can run any exe they want, if they chose to override the OS. You can do this by right clicking on an exe and choosing "Open" or you can go to the system preferences and turn off this feature. But typical "normal" users leave it on.
Let's check that SWMBO hasn't turned it off. Doug, go to System Preferences, then "Security & Privacy". Check that the section that says "Allow apps downloaded from" is set to "Mac App Store and identified developers".