I manage a Mac OS X (Leopard), laptop that has Norton Antivirus 11 installed. Whenever LiveUpdate executes, it proceeds to pull down a sig database of approx. 30 MB. Does anyone know why the updates aren't smaller ? I would've expected that Symantec downloads deltas of the databases. It is a concern as the user is a mobile user and does not always have high speed access.
It sounds like your LiveUpdate is broken. It is supposed to only give you "MicroDefinitions," also called "microdefs," which are updates to your existing definitions database (deltas).
There is a Symantec whitepaper (broken link) explaining this process (it references Windows, but LiveUpdate for Mac operates the same way).
Try installing the lastest updates manually from the NAV Definition Site, then run LiveUpdate again to see if it works this time.