Nessus is a freeware vulnerability assessment tool. Nessus works on a client/server based technology. The server side contains the vulnerability database and the engine that actually performs the vulnerability assessment. The client connects to the server to configure the settings for the vulnerability assessment. Nessus can provide reports in a number of different formats including its native GUI format, HTML, and ASCII. Nessus can be obtained at http://www.nessus.org.