Depending on the alert level, Windows Defender might automatically take action for you, or let you decide how to handle it.

For more info about the different alert levels, see Understand Windows Defender alert levels. If Windows Defender detects a potential threat, it notifies you and assigns an alert level to the threat. Windows Defender monitors when apps start and what operations they perform while running to help protect your PC. For example, spyware can run in the background when you start an app. Some malware looks for vulnerabilities in the apps that you've installed. Windows Defender scans your downloads to make sure they don't contain malware. However, malware might be included with these files and installed without your knowledge.

Many files and apps work with web browsers and can be downloaded, installed, or run by the browser itself.

Any files you try to download, run, or access.

Windows Defender monitors several things on your PC in real time: Real-time protection notifies you right away, whenever suspected malicious software (malware) or other potentially unwanted software tries to install itself or run on your PC. You can choose what data Windows Defender should scan anytime, or you can use real-time protection.

Windows Defender is installed as part of Windows and helps protect your PC from viruses, spyware, and other threats.

Windows defender for 8.1