Block apps will detect PUA that you've already downloaded or installed, so if you're using a different browser Windows Security can still detect PUA after you've downloaded it.

It is recommend that you turn this feature on, and that you enable both block apps and block downloads. Potentially unwanted app blocking was first introduced in Windows update, and is turned off by default. Windows Security has reputation-based protection that can help protect your PC from potentially unwanted applications.

Evasion software: Software that actively tries to evade detection by security products, including software that behaves differently in the presence of security products.

Also, software that offers to install other software that qualify as PUA.

Bundling software: Software that offers to install other software that is not digitally signed by the same entity.

Advertising software: Software that displays advertisements or promotions, including software that inserts advertisements to webpages.

PUA can also refer to an application that has a poor reputation, as assessed by Microsoft Defender ATP, due to certain kinds of undesirable behavior.

Potentially unwanted applications (PUA) are not considered viruses, malware, or other types of threats, but they might perform actions on endpoints which adversely affect endpoint performance or use. Potentially unwanted applications (PUA) are a category of software that can cause your machine to run slowly, display unexpected ads, or at worst, install other software which may be more harmful or annoying.

Starting with Windows 10 version 2004, Windows Defender Antivirus as been renamed to Microsoft Defender Antivirus.

How to Enable or Disable Microsoft Defender Antivirus Potential Unwanted App (PUA) Protection in Windows 10

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