^^^ norton might as well be spyware for all I'm concerned.
http://www.hijackthis.de/ <--- if you still have problems, try running this to see where the hijack is occuring. if you are confident enough in yr abilities, you can then edit the registry yrself.
also, up until the latest update, there was a nasty hole in flash that would allow you to become infected (on a PC) through ads on website.
if you do not run a mac, try using firefox with the no-script addon enabled.