NIS 2014 Live Update - Virus Definitions 150+mb every 2-3 days

NIS 2014, win xp sp3

 

Hi and thanks in advance.  I run Live Update manually every night and noticed the updater downloading large file sizes every few nights.  They are always Virus Definitions @ 150+ MB sizes.  I tried removing NIS with the removal tool and reinstalling (have 2013 CD, then update to 2014 through new version check online), but the problem came back after a few days.  What I would like to know is:

 

1)  Are the large file sizes and frequency of the Virus Definitions normal?

2)  What factors can cause this, if abnormal?

3)  How do I fix it?

 

Thank you for your help.