Windows Defender (Microsoft Defender Antivirus)

Microsoft Defender Antivirus is the free, built-in security solution for Windows 10 and 11. It provides real-time protection against viruses, malware, and ransomware (via Controlled Folder Access).

Integrated with the Windows Firewall and SmartScreen for web protection, it offers a competent, no-cost baseline. Its target audience is casual users with good computing habits who prefer a minimalist, integrated solution. It ranks for being completely free, deeply integrated into Windows for low system impact, and having improved dramatically to offer respectable, lab-tested protection that makes it a viable option for many.