Huge download

I've had Norton Internet Security '09 for almost 4 years, with annual renewals and no major problems for most of that time.  Suddenly I'm faced with an update of 210 MB -- an unprecedented size.  (They're usually not much more than 2 MB or so.)  Can this be correct, and any idea what's going on?  I'm on dialup;  a download of this size would take about a week to complete.  In practice it disconnects after a while, or the laptop (w/ Vista Home Premium)  gets too hot and shuts down.  

 

I tried submitting the basic question on the Norton help form but got a list of irrelevant topics in reply.

 

BTW, another odd thing I noticed is that it says my last definition update was 2 days ago  -- about when this thing started.  (Though that could be because I've been turning on Silent Mode a lot lately, in order to be able to use the laptop at all...?)