Cybersecurity

Cyberattack Knocks Out Access to Websites

Attackers controlling a vast collection of internet devices unleashed several massive attacks on Friday that left dozens of popular websites, including Twitter Inc. and Netflix Inc., unreachable for parts of the day.

Web-technology provider Dynamic Network Services Inc., known as Dyn, said its domain-name-system services were subject to a massive denial-of-service attack starting at 7:10 a.m. EDT on Friday. After the first onslaught was resolved, Dyn reported another wave of attacks that caused disruptions through the day.

Distributed denial-of-service attacks can knock websites offline by flooding them with junk data, blocking the way for legitimate users. Dyn’s DNS services are a key part of the digital supply chain that allows web addresses—Twitter.com, for instance—to take users to their destinations.