A port scan or port scanner attempts to connect to all 65536 ports on a server to see whether there are services listening (that is, waiting for connections) on those ports. The purpose of a port scan is to audit network computers for likely vulnerabilities or exploits. Typically, scanners have built-in databases of known port vulnerabilities.
A number of network scanners exist. For example, the Infiltrator Network Security Scanner tool reveals and catalogues a number of important security features, such as installed software, Simple Network Management Protocol (SNMP) information, and open ports. It can audit password and security policies and conduct a registry audit, and it includes 18 network utilities for footprinting, scanning, and gaining access to computers via a ping sweep, email tracking, whois lookups, and so on.
Also, the port scanner (formerly known as port probe) is a tool for determining the daemons or open ports running on a targeted computer. This tool supports these kinds of scans: TCP Full Connect (the most accurate way to detect open ports); UDP ICMP Port Unreachable Connect; TCP Full/UDP ICMP Combined; TCP SYN Half Open (only for Windows 2003/XP/2000); and TCP Other (only for Windows 2003/XP/2000).
The de facto standard in the security industry is a public domain tool called nmap, which is considered to be the “Swiss Army knife” of port scanners because of its versatility.
NorthWest Performance Software, Inc. NetScan Tools Pro Technical Info. [Online, May 18, 2005.] NorthWest Performance Software, Inc. Website. http://www .netscantools.com/nstpro_port_scanner.html; WebAttack, Inc. Infiltrator Network Security Scanner 2.0. [Online, May 18, 2005.] WebAttack, Inc. http://www.snapfiles.com/features/ infiltrator-803-461696.php.