I like Norton AntiVirus. The UI is OK, the protection is strong, and it doesn't get in my way. But its worm blocking doesn't play nice with FileZilla, the FTP client. When I'm uploading thousands of little files via FTP the worm blocker goes nuts.
I think the problem is that FTP still uses the awful non-PASV mode, where the server opens a socket back to my FTP client. Dumb, but that's the way FTP works. The worm blocker sees the incoming connections and assumes we're under attack. Fortunately it's easy to disable on a per-program basis with "Program Control" in "Internet Worm Protection". I see I've also disabled the checking for Half Life 2 and my X server. Guess this worm blocker doesn't like anyone opening connections to it.
The blocker is slow too. After I disabled it my FTP upload of lots of little files was 10x faster.