Built-in protection: Windows Security and macOS XProtect
What Microsoft and Apple say their own systems already include.
Windows Security
Microsoft says the Windows Security app is built into Windows and includes Microsoft Defender Antivirus, Windows Firewall, and Smart App Control.
Microsoft Defender Antivirus
Microsoft says Microsoft Defender Antivirus "continuously scans your device for potential threats." Microsoft's online scams page says Windows 10 includes it and it is turned on by default.
Checking it on Windows
Microsoft says to search for Windows Security in the Start menu, then open Virus & threat protection to run a quick scan or manage settings.
XProtect on a Mac
Apple says macOS includes built-in antivirus technology called XProtect, which detects and removes known malware using signatures. Apple says it updates those signatures automatically, separate from system updates.
What XProtect does when it finds malware
Apple says that when XProtect detects known malware, "it blocks it and moves it to the Trash," then alerts the user in the Finder.
Other software
Microsoft's support page notes there are also third party antivirus apps you can choose from. We do not say whether you need one; compare what each adds to what you already have.
This is general information, not security or technical support advice.
Sources: Microsoft Support, Stay protected with the Windows Security app; Microsoft Support, Protect yourself from online scams and attacks; Apple Platform Security, Protecting against malware in macOS.
FAQ
Next: what antivirus does
Known patterns, and the limits.
