For more details, see Announcing Microsoft Defender ATP for Mac and new Threat and Vulnerability Management capabilities | Microsoft Security Blog
"Microsoft is bringing its Windows Defender anti-malware application to macOS—and more platforms in the future—as it expands the reach of its Defender Advanced Threat Protection (ATP) platform. To reflect the new cross-platform nature, the suite is also being renamed to Microsoft Defender ATP, with the individual clients being labelled "for Mac" or "for Windows."Microsoft ships antivirus for macOS as Windows Defender becomes Microsoft Defender | Ars Technica
macOS malware is still something of a rarity, but it's not completely unheard of. Ransomware for the platform was found in 2016, and in-the-wild outbreaks of other malicious software continue to be found. Apple has integrated some malware protection into macOS, but we've heard from developers on the platform that Mac users aren't always very good at keeping their systems on the latest point release. This situation is particularly acute in corporate environments; while Windows has a range of tools to ensure that systems are kept up-to-date and alert administrators if they fall behind, a similar ecosystem hasn't been developed for macOS."