When Security Essentials is running on your computer, it automatically alerts you if it detects viruses, spyware, or other potentially unwanted software. You can also set Security Essentials to alert you if you run software that has not yet been analyzed, and you can choose to be alerted when software makes changes to your computer.
To set up Security Essentials alerts
Click Settings, and then click Real-time protection.
Make sure the Turn on real-time protection (recommended) check box is selected.
Select the check boxes next to the real-time protections options you want to run, and then click Save changes. If you're prompted for an administrator password or confirmation, type the password or confirm the action.