https://www.us-cert.gov/ncas/alerts/TA16-288A

This attacked was perpetrated by malware that infected internet connected devices (cameras, home wireless routers ect) with poor security. If you haven’t changed the default credentials of your router. You really should, seriously. Go follow the steps listed in the link above and fix your router and any web connected devices you have.

This attack was massive in scale, Dyn was getting hit with over 20T per second of spam. That is an insane amount of traffic that would pretty much bring down anyone.