GLOSSARY: DoS and DDoS

DoS

A Denial of Service attack is analogous to a group of people crowding the entry door of a shop, making it hard for legitimate customers to enter or leave the shop, thereby disrupting trade.

A denial-of-service attack (DoS attack) is a cyber-attack in which the attacker makes a machine (or network) unavailable to its intended users by temporarily (or indefinitely) disrupting services of a host connected to a network.

Often this is done by flooding the targeted machine (or network) with superfluous requests to overload systems and prevent legitimate requests being fulfilled effiiciently.

DDoS

In a distributed denial-of-service attack (DDoS attack), the incoming traffic flooding the victim originates from many different sources.

More sophisticated strategies are required to mitigate this type of attack, as simply attempting to block a single source is insufficient because there are multiple sources.

Revenge, blackmail and hacktivism can motivate these attacks - criminal perpetrators of DoS attacks often targeting sites or services hosted on high-profile web servers such as banks or credit card payment gateways to big corporations.

In early 2000, a Canadian teenager launched a series of distributed denial-of-service (DDoS) attacks against several high-profile websites. The teen, using the handle Mafiaboy, targeted Yahoo, ETrade, Dell, eBay, Amazon, and other sites over the course of several days, flooding the sites with massive amounts of junk traffic until their servers crashed. Although Mafiaboy (whose real name is Michael Calce).

Security experts warned in the aftermath of this episode that although he didn't use a 'botnet' for this devastating attack - botnets — and the DDoS attacks they're used for — posed a major threat to the stability and integrity of the Internet. Those experts turned out to be correct in the following decade.