Symantec Service Framework frequently using 50% of CPU

I have Norton Internet Security installed, v16.8.0.41, with Windows Vista, 3.0 GB of memory, and 2.33 GHz processor. 

 

3-4 times per day (or more) the CPU cranks up on my machine, and typically about 50% of it is due to Symantec Service Framework.  What is the reason behind the CPU increase?  Is it multiple downloads of virus definitions?  Updates to NIS?  Is there something I can do?