Apple macOS apps that have been downloaded from the internet and run at least once can be swapped with malicious versions, a pair of researchers say, calling into question the thoroughness of the company's "Gatekeeper" defenses. As Apple explains, "When a user downloads and opens an app, a plug-in, or an installer package from outside the App Store, Gatekeeper verifies that the software is from an identified developer, is notarized by Apple to b…