Denial of Service (or DoS) attacks are a form of network abuse that are often launched against companies or prominent websites. Their aim is to prevent access to a particular service that the site offers, such as online banking, email, or even just a general website. DoS attacks usually originate from computers infected with worms or trojans, and are choreographed remotely by the attacker.

Sometimes, the DoS attack is unintentional. One website, a techie news site called Slashdot, is renowned for these “attacks”, caused when the mention of a website in one of its news reports is accessed by all of its readers at once. As Slashdot is the most popular site amongst techies and nerds everywhere, the sheer amount of traffic overloads the website's server or network, preventing access to it.

DoS attacks can also be a form of protest; several have been launched against computer companies who have taken legal action against copyright violators or hackers.