The issue has since been mitigated.
DYN has restored service after a distributed denial-of-service (DDoS) attack against its DNS infrastructure took down Spotify, Twitter, and a host of other sites.
The internet performance management company published a statement on its status page explaining that a DDoS attack was responsible for the service interruption:
“Starting at 11:10 UTC on October 21st-Friday 2016 we began monitoring and mitigating a DDoS attack against our Dyn Managed DNS infrastructure. Some customers may experience increased DNS query latency and delayed zone propagation during this time. Updates will be posted as information becomes available.”