Learn how to Turn On, Enable or Start Windows Defender manually on a Windows computer. If it doesn't help, you may need to troubleshoot the issue.

You can now detect and block harmful third-party apps using Windows Defender Antivirus, and in this guide, we'll show you how to do it on Windows 10.

Microsoft releases Windows Defender extensions for Chrome and Firefox The add-on will still use Edge to open untrusted URLs, though.