Norton Internet Security uses some less than foolproof methods to try and block adverts. They also put at risk the funding of many small sites by doing this.

http://digitalimagesdesign.com/norton.htm

Don't know about you but I don't have any problem with the traditional 120x60 tile. It's the fullscreen, pop-up-in-front-and-take-over-your-browser adverts that need to be stamped on.