If you use Microsoft's free and excellent anti-virus and anti-spyware product "Microsoft Security Essentials (MSE)", you might already know that it updates its virus definition files using Windows Automatic Update.

If you have disabled Windows Automatic Update, MSE will not update the virus definitions. Then what to do in this case?

Don't worry! In this topic, we'll tell you how to update MSE virus definitions using a built-in MSE command? You don't need Automatic Update enabled to use this command.

=> Simply provide following command in Command Prompt or Startmenu Search box or Run dialog box:

"%programfiles%\Microsoft Security Essentials\MpCmdRun.exe" SignatureUpdate

It'll open a Command Prompt window which will show you a message "Signature update started...". It might take a few minutes depending upon the size of virus definition files.

You can also create a shortcut for the command and place it on Desktop or Quick launch toolbar or pin it to Windows 7 Taskbar. You can even schedule a task for the above mentioned command using Windows Task Scheduler.