Hi,
This is a known product issue and is scheduled to be resolved in Maintainance Release 1 which is targeted to become available some time between mid to late December 07.
Two potential steps that can ease the logging are:
1) The log entries are directly tied to a specific Liveupdate plugin which can run at every Symantec Endpoint Protection client heartbeat interval by default. This interval is configured in the console on the Clients page, highlight the group, click Policies tab, then click Communication Settings. Note, increasing the value will decrease the frequency with which you receive these Liveupdate log entries but you also need to be aware that it will also decrease the frequency with which you receive logging from the client.
2) You can schedule Liveupdate to automatically download definitions once per day. This will cause the LiveUpdate service to make entries to the System Event Log every four hours (18 entries per day in all, rather than hundreds.)
I realise this is far from ideal, but like I said, we are very much aware of this issue and will be delivering a fix soon.