Definition: denial-of-service attack

An assault on a network that floods it with so many requests that regular traffic is either slowed or completely interrupted. Unlike a virus or worm, which can cause severe damage to databases, a denial of service attack interrupts network service for some period.

Distributed Attack
A distributed denial-of-service (DDOS) attack can employ hundreds or even thousands of computers that have been previously infected. The computers act as a network of "zombies" working together to send out bogus messages, thereby creating huge volumes of phony traffic.

In 2016, the Dyn DNS system was hammered by a DDOS attack that caused sporadic slowdowns of major sites such as X/Twitter, Netflix and The New York Times. The zombie traffic reached more than 100 gigabytes per second of bogus messages. See botnet, mail bomb, smurf attack, SYN flood attack, land attack, booter service, teardrop attack and Ping of Death.

It's Not a New Phenomenon

In February 2000, computers were activated that had been previously hacked and planted with illicit programs. The unending number of requests caused a denial of service at Yahoo!, eBay, Amazon.com and other websites. (Article headline courtesy of the Philadelphia Inquirer.)