What is a denial of service attack (Dos attack)?

A denial of service attack is in the computer field defined as a cyber-attack in which the perpetrator seeks to make a network unavailable to users. Find out more in this article.

 Manifestations of a denial of service attack

Denial of service is achieved by flooding a targeted machine or source with unnecessary requests in order to overload systems and prevent the execution of some or all legitimate requests. It is sometimes carried out over the internet.

In a distributed denial of service attack, incoming traffic floods the victim from many different sources. It is then impossible to stop the attack by blocking a single source. This type of attack can be compared to a group of people crowding the front door of a shop, making it difficult for legitimate customers to enter the shop and disrupting service.

The perpetrators of these attacks usually target sites or services hosted on high-profile web servers such as banks or credit card payment gateways. These attacks are often motivated by revenge, blackmail and many other reasons.

 Symptoms of and fight against denial of service attacks

Several symptoms characterise a denial of service attack such as the unavailability of a particular website, or the inability to access any website. There is also an abnormally slow network performance (opening files or accessing websites)

This type of attack is often difficult to stop. Defensive responses to denial of service attacks usually involve using a combination of attack detection, traffic classification and response tools to block traffic they identify as illegitimate and allow traffic they identify as legitimate.

Denial of service attacks are a real problem in the IT world. Nevertheless, measures and countermeasures are being put in place to effectively combat the threat.