You can keep track of how your PC is doing by looking at the Microsoft Security Essentials icon in the notification area at the far right of the taskbar. Green means everything is okay, yellow means that your PC is potentially unprotected, and red means that your computer is at risk.
When you see yellow or red, click the icon and you’ll be able to see the details and take actions. Usually the best thing to do is to choose Clean computer so that the threat can be removed.
Microsoft takes on global cybercrime epidemic in tenth malware disruption. Following Monday’s multi-national action against the GameOver Zeus botnet, Microsoft is working closely with the FBI and industry partners to remove malware, so that infected computers can no longer be used for harm... Read more at 'Microsoft Digital Crimes Unit Newsroom'.
Sourced from http://www.microsoft.com/en-us/news/presskits/dcu/