To maximize the scan's effectiveness, you should make sure the computer is scanned using the very latest virus and spyware definitions, which contain the latest updates on potential threats.
To make sure the scan is using the latest virus and spyware definitions
Click Settings, and then click Scheduled scan.
Make sure the Check for the latest virus and spyware definitions before running a scheduled scan check box is selected, and then click Save changes. If you're prompted for an administrator password or confirmation, type the password or confirm the action.