Sixth in our IT security audit tools list is Nessus. This tool started off as a free, open source scanner, but now has a nominal cost attached to the professional version. A limited-utility free home edition still exists. Nessus was initially designed for Unix systems, but is now available for Windows too. The Nessus IT security audit tool mainly checks for the presence of default passwords; most commonly used passwords from the dictionary; any forms of misconfiguration; crafty packets within the networks; and, denial of service attacks. Nessus is handy for performing an audit and assessing the vulnerability ratio of the network.
You can download this tool here.