Nessus is the premier enterprise remote security scanner that simultaneously finds the latest security risks, performs TCP port scans, searches for network services, and provides comprehensive scan reports of all hosts on a network. Nessus version 3 is now distributed as a binary, so download the Macinitosh .dmg binary image and perform a standard "easy" install. No HOWTO is needed, just use the user-friendly Nessus GUI. To learn more about Nessus you may refer to the documentation.