A method used by individuals to break into a network to see which assets or services they can hi-jack for their own use or sabotage to limit their use by someone else.

A port scan essentially consists of sending a message to each port, one at a time, and monitoring what kind of response, if any, is received. The type of response indicates whether the port is used and can therefore be exploited further.

Since network services are normally associated with a “well-known” port number which provides access to it, a port scan can effectively identify which network resources can be exploited further.