Microsoft Defender

Microsoft Defender was known as Windows Defender before Windows 10 May 2020 Update. Windows Defender was originally released by Microsoft in 2005 as an anti-spyware program, the result of one of its many acquisitions in the security space. For seven years it functioned as Microsoft's free antispyware program, available for download from Microsoft's web site and sometimes bundled with Windows.

Windows Defender helps keep computer device safe from malicious or unwanted software. It’s always on, protecting the device, and pretty much runs by itself.

Windows Defender is a signature-based antimalware system, and these signatures provide the definitions that Windows Defender uses to identify malware on a Windows system.

These signatures provide information about current spyware and other forms of malware. The signatures provide information about the spyware images themselves and also the types of changes the spyware makes to an infected system.

In Windows 10 and later, the Windows Defender app is part of the Windows Security.
Microsoft Defender