Reback,
I believe Ron and Jens answered your question but hey, I gotta keep up my post count.
Yes NAV CE can be configured to automatically download the pattern via LiveUpdate, but that comes only once a week. IMHO, a week is a long time in virus years. Unlike Ron, I'd rather take my chances with a new VDB than risk waiting a week for a new pattern.
True, if a level 3 or greater threat comes out Symantec will release their LiveUpdate earlier, but I'd hate to be part of the level 3 statistic. Also, unlike Ron, who runs NAV corporate wide potentially affecting thousands of machines, I run a small divisional shop of 300 clients and can afford the risk of a pattern file shutting me down.
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Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.