bnbc, welcome to AnswerPool.com!
I assume that you're receiving this message when you're getting your email or when visiting a Web site. Does it ever pop-up when you're "off-line" (not connected to your Internet Service Provider)?
Do you use any of the Peer-to-Peer file sharing programs, like Kazaa?
If you're not running a firewall, I suggest you download and install the free (for non-commercial home use) ZoneAlarm.
Click HereAlso, it would be a good idea to verify that you've got the latest "Critical Updates" from Microsoft. In Internet Explorer, you can click the "Tools" menu, then the "Windows Update" command. It is also available in the Start Menu, "Windows Update" command.
Any information that you can provide about when and how this Norton message pops up would be helpful. And please let us know what Operating System and Web browser program you're using.
This page will help you gather this information.
I hope something here helps!
Dwight