Seems to be doing a full def download every day

I've just put Norton 360 on my W7 pc loaded from CD. Tuesday once loaded it then proceeded to download what I assumes were updates 400mb worth, reasonable. Wednesday after using the m/c for a few hours it then proceed to again download about 400MB again. I know it was Norton doing this because I found a network monitor showing N360 was the download application.

Thursday after about 1 hour of use it starts again this time it downloaded about 100MB before I dropped the connection.

Friday it's downloaded again more then 400MB. I've now turned off liveupdate and I'll manually download the update once a week.

Why is it downloading the complete update file instead of the incremental update??
I only have a mobile connection and so when this starts my internet connection is unusable until it has finished, is this typical of Norton download requirements.
I only use a 15GB 365 day plan and if this keeps up I will have to remove it before it uses up all my data allowance.
Also I cannot now find the window I used to monitor the download (I think it was a Norton 360 window) can anyone point me in the right direction.