What internet security/anti-virus/firewall software is there for Mac OS X v10.5 (Leopard)?

ClamXav is a free virus checker for Mac OS X. It uses the tried, tested and very popular ClamAV open source antivirus engine as a back end.

http://www.clamxav.com/

It’s pretty simple to understand why there are more viruses on Windows than on OS X: more people use Windows than OS X. Hackers generally target the biggest nail in order to reach a much larger audience.

There is no such thing as a “perfect” operating system. As more people move to mac computers, so do more hackeres exposing the security flaws.

Mac OS X Security Software