Go to the downloads section and click on the downloaded file to install Windows Defender definitions. Follow the prompts given by the installation wizard to update the Windows Defender.

How do I manually update Windows Defender?

Open the Settings app. Go to Update & security -> Windows Update. On the right, click Check for updates. Windows 10 will download and install definitions for Defender (if available).

Is Windows Defender still updated on Windows 7?

Windows 7 is no longer supported and availability of new installations of Microsoft Security Essentials has ended. We recommend all customers move to Windows 10 and Windows Defender Antivirus for our best security option.