mac and security

Hi
I would be grateful for any advice on whether it's necessary to install anti-virus etc software on a mac. Friends who have Macs don't seem to have anything installed. What are people's thoughts? If the answer is yes, instal, then what AV is recommended?
Ta

Personally I don't bother with any additional security software on my Mac (I do use NAT and a firewall via my router), any more than I do with my other Unix-like installations. But I do run anti-virus software on my Windows PCs.

It is not that I think that these systems are inherently that much more secure than Windows, it's just that I perceive the threat as being less (as they are far-less widespread than Windows and far fewer people know how to program them) and the facilities provided to detect intrusion are better.

This may change in time, should Macs ever become much more popular than they now are, but I feel secure with my current setup.

If you want AV ClamX will do the trick and stop you infecting PC friends.

Another vote for ClamXav here - it's donation ware so pay as much or as little as you like. ClamXav will run quietly in the background and/or on demand. The only virus i've ever seen on a Mac was one ClamXav caught in a Windows VISTA virtual machine