Update file size

I run Windows XP SP3, and I've been using NIS 2011 for 3 months now.  Most of the time updates download without trouble, and are a few KBs to 2 or 3 MBs in size.

 

Every so often, say once or twice a week, virus updates fail to download successfully, and when I retry I get an update greater than 90MB

.

This happened again today, and when I look at the details of this most recent large update under history, the 91 meg comprises only 3 files - 2011 whitelist, safe web stats, and puls updates.

 

This happens with both auto and manual updates. I turned off auto updates about a month ago, and run them manually now 2 or 3 time a day 7 days a week, so I can moniter the situation.

 

Can anyone tell me why this happens? My problem is, it's using up an awful lot of my monthly 2 gig allowance.

 

I currently have Smart Definitions set to off (default setting). System Status  = Secure. And generally all appears to be as it should be.