The Nessus vulnerability scanner is the world-leader in active scanners, featuring high speed discovery, configuration auditing, asset profiling, sensitive data discovery and vulnerability analysis Nessus performs sophisticated remote scans and audits of UNIX, Windows, and network infrastructures. Nessus discovers network devices and identifies the operating systems, applications, databases, and services running on those assets.

Up-to-date security vulnerability database
we mostly focus on the development of security checks for recent security holes. Our security checks database is updated on a daily basis, and all the newest security checks can be retrieved with the command nessus-update-plugins. An RSS feed of all the newest security checks allows you to monitor which plugins are added and when.

Remote And local security
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  is the only security scanner out there which 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.

Plug-ins
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. Each NASL plugin can be read and modified, to better understand the results of a Nessus report.

NASL
The Nessus Security Scanner includes NASL, (Nessus Attack Scripting Language) a language designed to write security test easily and quickly. NASL plugins run in a contained environment on top of a virtual machine, thus making Nessus an extremely secure scanner.

Smart service recognition
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. Nessus is the first scanner on the market to have implemented this feature for all the security checks (and has been copied by many since then).

Multiples services
If a host runs the same service twice or more, Nessus will test all of them. Believe it or not, several scanners on the market still consider that a host can only run one server type at once.

Full SSL support
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. Once again, Nessus was one of the first security scanner on the market to provide this feature.

Non-destructive OR thorough
Nessus gives you the choice between performing a regular non-destructive security audit on a routinely basis, or to throw everything you can at a remote host to see how will it withstands attacks from intruders. Many scanners consider their users to be too inexperienced to make that kind of choice, and only offer them to perform "safe" checks.

Proven maturity
Nessus is in use by the majority of Fortune1000 companies. The first public release of Nessus was in 1998. The technology behind it has been extensively tested and proven over time, on huge networks.