Although it’s not something casual internet users generally need to be afraid of, many people have heard of denial of service (DoS) attacks through the news. DoS attacks are also sometimes called distributed denial-of-service attacks (DDos), and are often used to disrupt website service and thus make it inaccessible to users.
To understand a DoS attack, you must first understand that whenever you access a website, your browser requests the information from the server which is hosting that website. If the site is receiving a normal amount of traffic, it will be able to cope with the multiple requests for data, however if there is a big enough surge of requests, the server may not be able to cope with them all and might crash. Sometimes these surges happen spontaneously because of a shocking piece of breaking news, or some other factor which may draw many users to a particular website at once. In the case of a DoS attack, though, the sudden demand which disrupts service is completely intentional.
Whilst it takes a lot of computers to completely crash a server, this does not mean that a DoS attack is performed by hundreds or thousands of hackers concentrating on the same attack together. Instead it can be orchestrated by only one hacker using a network of “zombie computers”. These zombie computers typically have malware installed on their system which allows hackers to control the requests they send out over the internet. With the zombie computers in his control, a hacker can inundate his chosen website with so many requests that the server crashes and service is disrupted for genuine users of the site.
Motivations for a DoS attack vary from person to person; the attack has been used both to play disruptive pranks on ‘rival’ sites and to totally block access to government websites as a political statement.