No one has claimed responsibility, and Dyn has been somewhat quiet about the attack vectors, but has said that possibly 100,000 hijacked connected devices could have been used in the attack.

The attacks could be fallout from the Mirai IoT Botnet assault against Brian Krebs earlier this month. As Krebs himself notes, the attacks started within hours of a DynDNS researcher, Doug Madory, presenting a talk (video link here) at NANOG about DDoS attacks. Also, according to Krebs, the 620GB Mirai attack against krebsonsecurity.com came just hours after he and Madory released an article looking into some of the shady dealings in the DDoS-for-hire industry.