Port scanners provide a first step toward detecting and discovering the services and network applications listening on your network. When faced with an unknown computer, programs such as the free Foundstone SuperScan 4.0 and the open-source port scanner Nmap show you not only whether the typically used HTTP port TCP 80 is open, but also the response, or banner, of the listening application. I’m a huge fan of Nmap (see “Nmap 4.0 Does Windows,” InstantDoc ID 50062) and not just because of its scanning features: I like that Nmap runs from the command line and that its results come in a variety of formats, making the tool easy to incorporate into other scripts. In other words, Nmap is a great tool to integrate with all kinds of network-centric audits. Let’s look at how to leverage Nmap and its flexible output features to quickly determine whether antivirus software is installed on the computers within a subnet. . . .
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