Before installing Norton security software, first, remove existing software from Mac and then, go to the Norton Security Online page and click on Get Norton Security Online. Enter your Xfinity username and password if asked. Create your Norton account that lets you manage all of your Norton Services and products keys from an individual location. Now, click on Install and the installation process of Norton Internet Security Begins. Open your Mac downloads list after the installation finished. Double click on the Install file and run the installer. And follow the Mac in-built instructions to install it properly.
Any Norton information: http://www.norton.uk-help-number.co.uk/