I had the same concern. Here is the response to my query from Symantec:
Per your request I will try to explain the reason why it "appears" that your definitions are out of date:
Here is a cut and paste from
(Symantecs security response page).
Intelligent Updater Defs created March 5
Intelligent Updater Defs released March 5
LiveUpdate Defs released February 27
Norton AntiVirus Corp. Edition Defs Version: 40305a
Norton AntiVirus Corp. Edition Sequence Number: 15201
Norton AntiVirus for Mac Defs released February 28
Total Viruses Detected: 58980
The way that Liveupdate works (today as well as in the past) is that our Liveupdate servers are updated with new definitions every Wednesday unless a category 3 or higher virus outbreak occurs. If this happens, we will update the Liveupdate servers as soon as the definitions to catch the cat. 3 or higher virus are ready. The recent change that we have made deals with the intelligent updater which is now being released on a daily basis. If you choose to, you can download this file (available on our web site) and run it on the primary server to update your definitions on a daily basis. The only difference between the updates that Liveupdate retrieves and the the intelligent updater is that the intelligent updater contains definitions to catch the level 1 and 2 virus' that come out during the week. This is why, in the above cut and paste, you see a different definition date for Liveupdate and intelligent updater.
I hope this helps explain the situation
Thanks for calling Symantec
Todd Vinson, MCSE
Product Support Analyst
Symantec, Corp.
tvinson@symantec.com