Dyn offers Domain Name System (DNS) services, essentially acting as an address book for the Internet.
DNS is a system that resolves the web addresses we see every day, like https://www.WIRED.com, into the IP addresses needed to find and connect with the right servers so browsers can deliver requested content, like the story you’re reading right now.
Since Dyn says the impact was on its East Coast servers, this probably created the localized effect.
Initial reports indicate that the attack was part of a genre of DDoS that infects Internet of Things devices (like webcams, DVRs, routers, etc.) all over the world with malware, and conscripts them into botnet armies to then coordinate, generate, and amplify malicious traffic toward a target.
Dyn said on Friday evening that the security firms Flashpoint and Akamai detected Mirai bots driving much of the traffic in the attacks.