Windows Defender Antivirus is a built-in security program in the Windows operating system designed to protect computers from malware, viruses, and other security threats. It automatically scans files and applications for harmful content and provides real-time protection to help keep your system safe while you browse the internet or download files. In addition to its scanning capabilities, Windows Defender offers features like firewall protection, device performance monitoring, and parental controls. It regularly updates its virus definitions to stay current with the latest threats, ensuring that users have a reliable defense against cyber attacks without needing to install third-party software.