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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 services running on a host and exploit vulnerabilities. A port scan or portscan is a process that sends client requests to a range of server port addresses on a host, with the goal of finding an active port; this is not a nefarious process in and of itself. 〔RFC 2828 ''Internet Security Glossary''〕 The majority of uses of a port scan are not attacks, but rather 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 to search for a specific service, for example, an SQL-based computer worm may portsweep looking for hosts listening on TCP port 1433.〔http://support.microsoft.com/kb/313418〕 ==TCP/IP basic knowledge== The design and operation of the Internet is based on the Internet Protocol Suite, commonly also called TCP/IP. In this system, hosts and host services are referenced using two components: an address and a port number. There are 65536 distinct and usable port numbers. Most services use a limited range of numbers. Some port scanners scan only the most common port numbers, or ports most commonly associated with vulnerable services, on a given host. The result of a scan on a port is usually generalized into one of three categories: #''Open'' or ''Accepted'': The host sent a reply indicating that a service is listening on the port. #''Closed'' or ''Denied'' or ''Not Listening'': The host sent a reply indicating that connections will be denied to the port. #''Filtered'', ''Dropped'' or ''Blocked'': There was no reply from the host. Open ports present two vulnerabilities of which administrators must be wary: #Security and stability concerns associated with the program responsible for delivering the service - Open ports. #Security and stability concerns associated with the operating system that is running on the host - Open or Closed ports. Filtered ports do not tend to present vulnerabilities. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Port scanner」の詳細全文を読む スポンサード リンク
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