McAfee and Norton are both shady as hell, it's more than reasonable to suspect that they write viruses in order to boost their business. Fuck antivirus and insecure OS, Linux with no antivirus is the way to go.
(before any ignorant Windoze fanboys try to say it's because Linux has less marketshare, please do a little research on outward listening ports, Linux' kernel level security, and the anecdotal evidence that there really aren't any antivirus solutions for Linux).