Windows Defender Definition Updates for timely updating of your Windows Defender if the automatic update happens to fail.

Installation instructions for Windows Defender Definition Updates:

Step 1: Save or run the file

After you click this link, click Run to install the definition file immediately, or click Save to save it to your computer. If you click Save, remember the name of the folder where you save the file.

Step 2: Install the definition update

To install the saved definition update file:

If your computer is running Windows Vista, click Start, click Documents, and then locate the folder where you saved the definition file. Right-click Mpas-fe.exe, click Run as administrator and then click Run. When you are prompted for an administrator password or confirmation, type the password or provide confirmation, and then wait while the definition files are installed.

If your computer is running any other Windows operating system, you must be logged on as an administrator to install the latest definition file. Browse to the folder where you saved the file, and then double-click Mpas-fe.exe to install the latest definition file.
Note: If you do not have an administrator account on the computer, ask an administrator to log on and install the definitions file for you.

For more information on how to manually download the latest definition updates for Windows Defender, see this Knowledge Base article on the Microsoft Help and Support website.