and then depending on the alert level you can do one of 3 things
Remove—This action permanently deletes the software from your PC.
Quarantine—This action quarantines the software so that it can't run. When Microsoft Security Essentials quarantines software, it moves it to another location on your PC, and then prevents the software from running until you choose to restore it or remove it.
Allow—This action adds the software to the Microsoft Security Essentials allowed list and allows it to run on your PC. Microsoft Security Essentials will stop alerting you to risks that the software might pose to your privacy or to your PC.