Virus protection is not a priority on the Mac. I recommend it for disinfecting the files received from Windows-using colleagues. I firmly believe that Mac users should not pass on Windows viruses. The Mac viruses that are, date back mostly to System 6 and System 7. There are no MacOS X viruses. There are most certainly no viruses on Intel-based Macs--not even proof-of-concepts. Personally, I use Norton Antivirus for Macintosh 10, which I keep updated. It handles all known viruses, none of which can infect MacOS X. IIRC, NAM has yet to be updated for Intel-based Macs. One of the antivirus utility vendors--I forget which one--has updated its software for Intel-based Macs. The takeaway message is that installing antiviral software on your Mac is an act of good citizenship, but not doing so poses no threat to your own system.