A port scanner is a software application designed to probe a server or host for open ports. This is often used by administrators to verify security policies of their networks and by attackers to identify running services on a host with the view to compromise it.
A port scan or portscan can be defined as an attack that sends client requests to a range of server port addresses on a host, with the goal of finding an active port and exploiting a known vulnerability of that service, although the majority of uses of a port scan are not attacks and are simple probes to determine services available on a remote machine.
To portsweep is to scan multiple hosts for a specific listening port. The latter is typically used in searching for a specific service, for example, an SQL-based computer worm may portsweep looking for hosts listening on TCP port 1433.
Read more about Port Scanner: TCP/IP Basic Knowledge, Port Scanning Assumptions, Port Filtering By ISPs, Ethics, Legal Implications
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“The triumphs of peace have been in some proximity to war. Whilst the hand was still familiar with the sword-hilt, whilst the habits of the camp were still visible in the port and complexion of the gentleman, his intellectual power culminated; the compression and tension of these stern conditions is a training for the finest and softest arts, and can rarely be compensated in tranquil times, except by some analogous vigor drawn from occupations as hardy as war.”
—Ralph Waldo Emerson (1803–1882)