In computing, a denial-of-service attack (DoS attack)

In computing, a denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a machine or network resource unavailable to its intended users. Although the means to carry out, motives for, and targets of a DoS attack may vary, it generally consists of efforts to temporarily or indefinitely interrupt or suspend services of a host connected to the Internet.

Perpetrators of DoS attacks typically target sites or services hosted on high-profile web servers such as banks, credit card payment gateways, and even root nameservers. This technique has now seen extensive use in certain games, used by server owners, or disgruntled competitors on games. Increasingly, DoS attacks have also been used as a form of resistance. DoS they say is a tool for registering dissent. Richard Stallman has stated that DoS is a form of 'Internet Street Protests’.The term is generally used relating to computer networks, but is not limited to this field; for example, it is also used in reference to CPU resource management.

One common method of attack involves saturating the target machine with external communications requests, so much so that it cannot respond to legitimate traffic, or responds so slowly as to be rendered essentially unavailable. Such attacks usually lead to a server overload. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consuming its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.

Denial-of-service attacks are considered violations of the Internet Architecture Board's Internet proper use policy, and also violate the acceptable use policies of virtually all Internet service providers. They also commonly constitute violations of the laws of individual nations.

An intrusion detection system

An intrusion detection system (IDS) is a device or software application that monitors network or system activities for malicious activities or policy violations and produces reports to a management station. Some systems may attempt to stop an intrusion attempt but this is neither required nor expected of a monitoring system. Intrusion detection and prevention systems (IDPS) are primarily focused on identifying possible incidents, logging information about them, and reporting attempts. In addition, organizations use IDPSes for other purposes, such as identifying problems with security policies, documenting existing threats and deterring individuals from violating security policies. IDPSes have become a necessary addition to the security infrastructure of nearly every organization.

IDPSes typically record information related to observed events, notify security administrators of important observed events and produce reports. Many IDPSes can also respond to a detected threat by attempting to prevent it from succeeding. They use several response techniques, which involve the IDPS stopping the attack itself, changing the security environment (e.g. reconfiguring a firewall) or changing the attack's content.

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite (TCP/IP) to serve several billion users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies. The Internet carries an extensive range of information resources and services, such as the inter-linked hypertext documents of the World Wide Web (WWW), the infrastructure to support email, and peer-to-peer networks.

Intranet

An intranet is a computer network that uses Internet Protocol technology to share information, operational systems, or computing services within an organization. This term is used in contrast to internet, a network between organizations, and instead refers to a network within an organization. Sometimes, the term refers only to the organization's internal website, but may be a more extensive part of the organization's information technology infrastructure, and may be composed of multiple local area networks. The objective is to organize each individual's desktop with minimal cost, time and effort to be more productive, cost efficient, timely, and competitive.

撲克牌

撲克牌（Anglo-American playing card、 French deck），簡稱撲克，直譯為英美牌、法國牌，香港俗稱啤牌，是英國、美國、華人圈等地最常使用的遊戲牌牌具。、

麻雀、麻将、馬將或蔴雀

麻雀、麻将、馬將或蔴雀是一種源自中國的策略遊戲。遊戲參與者以四人居多，但也有二人、三人等變種（在日本、韓國較為常見）。麻雀在各地的規則（尤其是計分方法）有很大不同，但基本目標都是通過一系列置換和取捨規則拼出某個特定組合的牌型，并阻止對手達成相同目的。遊戲側重技巧、策略運用和計算，但也涉及相當多的運氣成份。比起撲克，麻將的組合方式更為變化多端，需要通過複雜的概率分析才能預測結果。但麻將需要記憶的規則和牌型也比一般撲克牌戲要多得多。在東亞與東南亞地區，特別是華人社區中，麻雀常被當做娛樂或賭博手段。

麻雀的牌張，各地大同小異，但多與廣東麻雀相同，或為其子集。廣東麻雀是迄今仍流傳的華人玩法之中，歷史最悠久者，其牌張分三類。第一類為序數牌（見附圖），分「筒子/饼」、「索子/条」、「萬子/萬」三門，每門有序數從一至九的牌各四張（三門共108隻）。第二類是字牌，包括「東、南、西、北」四款「風牌」及「中、發、白」三款「三元牌」，每款四張（七款共28張）。第三類是花牌，有「梅、蘭、菊、竹、春、夏、秋、冬」八隻。故全副麻雀共計有144張。古代麻雀有骨製、竹製或象牙製，現代麻雀則多以塑膠製成。

一副麻將除了牌張，還有骰子及其他道具，例如日本麻雀有「點棒」，廣東麻雀就有一件稱為「莊」的塑膠道具，用來識別莊家與顯示「圈風」。