I was thinking about ordering Norton Antivirus when I order my new iMac. But I can't really track down a reliable review of the product, and how it impacts on a modern iMac. ie. Does it slow the system down? So if there is any members who use Norton Antivirus for Mac, like to hear from you. I realize there is few Mac threats, I guess I want to keep my removable USB drives clean so that viruses don't spread between PC's mostly.