PT,
Antivirus definitions should almost be updated daily. Norton's 2003 version 
has an automatic update feature that does the update every time you sign on to 
your ISP.
I would also recommend installing spybot software 
http://www.safer-networking.org/index.php?page=mirrors and depending on the Windows version you are 
running also installing Zone Alarm which also has a free version to try out:  
http://www.zonelabs.com/store/content/home.jsp
It seems like a lot to do, but it is necessary in this day and age.

Rummy