VirusDefs folder is 25GB!? help required

Advice needed.

 

Over the past month i have been losing hard drive space at about 500mb per session.  I have followed a lot of advice [deleting restore points, hibernation settings, ccleaner etc] but after downloading jam softwares Tree size it came to my attention that the folder VirusDefs if about 25GB in size!!!

 

C://program files/common files/symantec shared/virusDefs/

 

 

could this be the reason? should it be that large? and can i delete it?

 

 

 

note: I have Norton Internet security 2005

 

thank you for your time