If a virus is detected, it will be stored in the session results, just as any other results. So, it won't be presented e.g. as a messagebox. The scheduled scans may be running even when nobody is logged on, so in general there may be no desktop to show the dialog on.
Of course, you can set an virus alert in the corresponding task - so you will be notified (e.g. by e-mail) when a virus is detected.