2009 DDoS attacks against South Korea

The July 2009 cyberattacks were a series of coordinated cyberattacks against major government, news media, and financial websites in South Korea and the United States. The attacks involved the activation of a botnet—a large number of hijacked computers—that maliciously accessed targeted websites with the intention of causing their servers to overload due to the influx of traffic, known as a DDoS attack.

Source: Wikipedia — 2009 DDoS attacks against South Korea (CC BY-SA 4.0)