Actually if u notice properly, norton is actually the one which
releases virus definations at a slower rate.. It usually updates
once a week.. every wed or thurs through liveupdate... But of
course, if u want extra protection, u can download the daily virus
definations from symantec website and apply it yurself manually..
But AVG antivirus updates itselfs every 2 days or so.. sometimes
daily too.. 
