Norton has historically been pretty bad with Trojans, so I'm not surprised by its failure here at all.
As Golden says, you should use at least two different products for malware protection
1) a traditional AV
2) an sepcialist malware scanner.
One of the problems with traditional AV's - particularly the big ones - is that malware can be, and is. designed to hide from the major players, or to function in ways that are outside the remit of such things.
Specialist malware scanners have a different take on their duties, and will flag things that AV's would not (such as adware), and use very different methods of detection. Because of this, they tend to catch a variety of things that may be ignored by AV's. Running a full Malware scan with such a beast also ensures that the AV gets a good look at all files as well - I've seen machines where an AV gives it a clean bill of health, but running a malware scan, the AV complains almost as much as the scanner as each file is opened and decompressed by the scanner, which may enable the AV to get abetter look at the true content of the file.
This is one reason why I do not ever purchase 'Suites' of such software - as I prefer to pick-and-choose. Currently all my machines use MSE as AV, and Malwarebytes Anti-Malware as the scanner. I'm delightged to say that MBAM actually picks up very little that gets past MSE - and I've not found anything significant when I've used other scanners as a double-check.
I don't visit as many potentially nasty sites as I used to - but I still on occasion deliberately do so to test that things are properly functional, and this pairing hasn't let me down yet, and has the great advantage of being free
