I'm not familiar with Norton's updating mechanisms I'm afraid.
You can control how it updates by doing the following...
Double-click the taskbar icon to open Security Center Click Advanced Menu (bottom left) Click Configure (left) With Security Center highlighted at top left Click Advanced (right) Click Update Options at left.
Usually it's just the DAT update daily for VirusScan, but occasionally other applications may update too, usually it all comes in at once so shouldn't be too obtrusive. SiteAdvisor for instance, if you use it in your browser, updates silently.