After you install Microsoft Security Essentials on your PC, you can close the main window and let it run quietly in the background. Microsoft Security Essentials will continue running on your PC, monitor it, and help protect it against threats.
Of course, you'll know that Microsoft Security Essentials is running when it displays messages in the notification area on the right side of the Windows taskbar. These notifications alert you to potential threats that Microsoft Security Essentials has detected.
You'll also receive other alert notifications when real-time protection has been turned off, or if you haven't updated your virus and spyware definitions for a number of days, or when upgrades to the program become available. Microsoft Security Essentials also briefly displays a notification to let you know that it's scanning your PC.
You can also refer to the Microsoft Security Essentials icon that appears in the notification area.
If you don’t see the Microsoft Security Essentials icon in the notification area, click the arrow in the notification area to show hidden icons.
The icon color depends on your PC's current status:
Green indicates that your PC's status is "protected."
Yellow indicates that your PC's status is "potentially unprotected."
Red indicates that your PC's status is "at risk."