What is difference?

Why Avast found 74,508 virus list at last up date? (about)
But Norton Anit virus found 71974 virus list at last update. 4/1/2006
What is difference?
Thank you.

Different av vendors use different meanings of counting.
This has been explaind before on this board.
Please use the search option before asking.

here
http://forum.avast.com/index.php?topic=18453.0