A few months ago, there was an article in PC Mag about a test of virus programs. MacAfee was rated top, AVG Free 7.5 was rated second (I'd use it... just search for AVG Free, you'll find a link at download.com). Norton was rated somewhere around 10th. Seriously. Norton is a big old heavy heaping helping of over-hyped software.
Our one PC (all our other computers are Macs) got this password-watching virus at home. Well, Norton didn't see it. *I* saw it because I glanced over at the screen and saw a DOS window pop up and it appeared to be FTP'ing to some IP address. I noted the name of the program and the IP address before the window disappeared. I force quit the program and found it on the hard drive. I copied it to my Mac over the network for further inspection in a text editor. I did a bit of research on how to remove it, and did so.
Later, I was browsing my Mac over the network, and Norton jumps up and yells at me, OMGWTH VIRUS FOUND!!! DELETED!!!
So it didn't see it when it wiggled its way onto my PC or when it was running, but it noticed the .exe sitting on my Mac desktop where I was keeping it to look at, *and* deleted it without even asking what I wanted to do with it! Oh well, I was pretty much done researching it by that point anyway but the fact was, it wasn't the actual virus.