Norton Internet Security uses Idle Time Scans to automatically detect the idle state of your computer and runs a Full System Scan when the computer is idle. However, you can schedule a Full System Scan according to your preferences. Norton Internet Security prompts you that the Idle Time Scans option gets turned off when you schedule a Full System Scan. You can also set up a schedule for custom virus scans.

You can schedule scans to run unattended on specific dates and times or at periodic intervals. If the scheduled scan begins when you use your computer, you can run the scan in the background instead of stopping your work. This option is available for a Full System Scan and for any custom scans that you create