I make sure everything is scanned before it is opened and I always make sure my AV is on and up to date... that trojan you have is 6+ months old.... not every AV removes the virus let alone fixes them chaos it has caused....
I personally dislike Norton products aimed at the home consumer....
Norton has a manual fix posted on their website to remove that trojan...
http://securityresponse.symantec.com...r.mscache.html