Several websites including Twitter and Tumblr were unreachable during an extended period for many U.S. internet users Friday following repeated online attacks. Web-technology provider Dynamic Network Services Inc., known as Dyn, said its domain name system, or DNS, service was subject to a massive distributed denial-of-service attack starting at 7:10 a.m. on Friday. After the first attack was resolved, Dyn reported a second one around midday. The service was spotty towards afternoon but was generally up by 4.30 p.m. Wall Street Journal
