XProtect.app appears to scan for known malware much more aggressively than the MRT did. As mentioned in Apple's most recent Platform Security documentation, this is a familiar name for a new app that replaces the old MRT.

Since around the release of the 12.3 update for macOS Monterey, he's been tracking a new 'XProtect.app' feature that has been added to Monterey, Big Sur (11), and Catalina (10.15). And he says that Apple's anti-malware tools have undergone a dramatic but mostly silent change over the last few months. Howard Oakley at the Eclectic Light Company makes a habit of tracking updates to XProtect and the MRT, and he maintains several utilities that check the versions of your definitions (as well as your installed firmware and other Mac esoterica that Apple regularly updates but rarely mentions). Another under-the-hood tool, the Malware Removal Tool (MRT), behaved more like a traditional anti-malware scanner, periodically receiving definitions updates from Apple so that it could scan for and remove malware already present on your system. Gatekeeper, app notarization, System Integrity Protection, the Signed System Volume, and access controls for hardware and software are all, one way or another, about proactively protecting system files from being tampered with and making sure that installed apps do what they say they're doing. Since then, Apple has added multiple anti-malware features to macOS, though they're not always branded that way. Called 'XProtect,' this system service downloaded and installed new malware definitions in the background in between major macOS security updates, mostly to protect against the installation of known, in-the-wild malware.

But Apple began to include rudimentary anti-malware protections in macOS starting with Snow Leopard in 2009. Macs don't have visible anti-malware software built-in, at least not in the same way that Microsoft does with Windows' highly visible Defender software. Further Reading Snow Leopard includes rudimentary malware protection (Updated)

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