There is a great deal of reading available about this, hours and hours. Just search this site. I'll try to net it down for you ....
First, Norton's has a rotten reputation in the mac world. I would avoid it.
Macs have pretty good security from the factory. OS X has a firewall, which you should ensure in System Preferences under sercurity and privacy, that it's enabled. In the firewall options, select enable stealth mode, too.
There are opnions about the need or non-need for antivirus software. Most agree, however, if you do use any, that ClamXav is the one to use (I've used it for years with no issues).