[aoetalks]

Not saying the rebrand makes sense, but this new product is called Microsoft Defender, while the one in Windows was called Windows Defender.

[saxonww]

Like Microsoft Update and Windows Update?

[derkades]

It used to be called Windows Defender, until they renamed it to Microsoft Defender some time ago

[Scharkenberg]

Yes, but that's precisely because they intended to ship a (newly) cross-platform product. From my understanding, the goal is that on Windows one is supposed to find Windows Security Center + Microsoft Defender or another antimalware software. Not fully modular but hotswappable.