A "vulnerability scanner" (sometimes called a "network analyzer") is a utility program that makes it possible to perform a security audit on a network by scanning for open ports on a given machine or an entire network. The scanning process uses probes (requests) that make it possible to determine the services that are running on a remote host.
Such a tool makes it possible to determine security risks. In general, with this type of tool, it is possible to launch an analysis over a range or a list of IP addresses in order to fully map a network.
A vulnerability scanner is capable of determining the ports that are open on a system by sending successive requests to the various ports and analyzes the responses to determine which ones are active.
By thoroughly analyzing the structure of TCP/IP packets received, advanced security scanners are sometimes able to determine the remote machine's operating system as well as the versions of applications associated with the ports and, when applicable, to recommend necessary updates - this is referred to as version characterization.
Two methods are generally used:
Security scanners are extremely useful tools for system and network administrators, letting them monitor the security of the computer population they are responsible for.