Denial-of-service attack

A denial-of-service (DoS) attack is an Internet-based attack in which the perpetrator deliberately overloads an individual’s or organization’s web servers by repeatedly accessing them, typically using an automated program. Such attacks generally aim to render a website or computer network inaccessible for a period of time. Perpetrators of denial-of-service attacks also sometimes target entire Internet service providers, affecting numerous websites at once. While some denial-of-service attacks are intended merely to inconvenience or annoy the owners or users of a website or network, such attacks are often used in the contexts of corporate sabotage, computer-based activism (or hacktivism), and cyberwarfare.

Overview

When an individual connects to a website, their computer sends a request to the server on which the site is hosted. The server then responds to this request, sending the information that makes up the requested page. Sometimes, however, too many people attempt to access a website at once, overloading the host server and thus causing the website to load slowly or not at all. DoS attacks purposefully replicate this process, rendering websites or entire networks inaccessible, often for malicious purposes.

DoS attacks are typically carried out using automated programs that send repeated requests to the target site or network, thus causing the server to overload. In many cases, perpetrators of such attacks use computer programs that infect random unsecured computers and run undetected in the background. When the perpetrator initiates a coordinated multicomputer attack, the programs hijack the resources of the computers they have infected and proceed to overload the target website or network. DoS attacks carried out using multiple computers are known as “distributed denial-of-service (DDoS) attacks.” In addition to overloading websites or networks, some DoS attacks seek to crash the operating system of the target server or render a target networking device, such as a router, completely unusable.

DoS and DDos attacks may be carried out for a wide range of purposes. In some cases, perpetrators simply attack websites for their own entertainment; in other instances, attacks serve larger purposes. According to a report released by the computer-security company NSFOCUS, in the first half of 2013, the most common motivation for DDoS attacks was computer-based activism, or hacktivism. Hacker activists often carry out DoS and DDoS attacks as a form of protest against governments, businesses, or organizations. Other major motivations for DDoS attacks included corporate sabotage, with some companies seeking to overload and incapacitate the websites of their competitors, and international cyberwarfare. Frequent targets of DDoS attacks include banks, governments, large corporations, nonprofit organizations, and Internet service providers. When Russia invaded Ukraine in 2022, it launched DDoS attacks against Ukraine's financial sector and other targets, such as the country's infrastructure. Ukraine retaliated and launched similar DDoS attacks against Russia.

Individuals and organizations seeking to reduce their vulnerability to DoS attacks have several options. In some cases, firewalls can be used to prevent specific Internet Protocol (IP) addresses—numerical addresses that identify particular Internet-connected computers—from accessing a site; this is most helpful when the attack is carried out by an individual or small group rather than a network of hijacked computers. Some companies or institutions may also choose to reevaluate the design of their networks and purchase backup equipment that can be used in the event of a DoS attack. A number of computer-security companies offer DoS/DDoS mitigation devices, which identify and block traffic that is deemed illegitimate.

Bibliography

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