Vote for Nessus Security Scanner

Traditional network security scanners tend to focus on the services listening on the network - and only on these. Now that viruses and worms are propagating thanks to flaws in mail clients or web browsers, this conception of security is getting outdated.
Nessus has the ability to detect the remote flaws of the hosts on your network, but their local flaws and missing patches as well - whether they are running Windows, Mac OS X or a Unix-like system. Each security test is written as an external plugin, written in NASL. This means that updating Nessus does not involve downloading untrusted binaries from the internet. The Nessus Security Scanner includes NASL, (Nessus Attack Scripting Language) a language designed to write security test easily and quickly. Nessus does not believe that the target hosts will respect the IANA assigned port numbers. This means that it will recognize a FTP server running on a non-standard port (ie: 31337), or a web server running on port 8080. If a host runs the same service twice or more, Nessus will test all of them. Nessus has the ability to test SSLized services such as https, smtps, imaps, and more. You can even supply Nessus with a certificate so that it can integrates into a PKI-fied environement. Nessus gives you the choice between performing a regular non-destructive security audit on a routine basis, or to throw everything you can at a remote host to see how will it withstands attacks from intruders.