Twitter, Reddit, Spotify, and SoundCloud were among sites affected by a massive cyber attack earlier today, as TechCrunch reports. The hack also affected The Boston Globe, The New York Times, Github, Airbnb, Vox Media sites, Shopify, and others. Users of Netflix and PayPal also said they were experiencing problems, the Times reports. The sites were down or otherwise interfered with amid a big “distributed denial of service” (DDoS) attack on the servers of Dyn, a company that ensures Internet traffic gets where it is trying to go. Dyn said the problem mainly affected users in the eastern United States and that services were restored to normal around 9:20 a.m. ET, but then another attack took place around 11:52 a.m. ET. “Our engineers are continuing to work on mitigating this issue,” the company said, later adding there “several” attacks. Dyn hosts Domain Name Services (DNS), which are often compared to a phone book or map of the Internet.

Here's what Dyn said earlier about the problem: “Starting at 11:10 UTC [7:10 a.m. ET] 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.”

The U.S. government is investigating whether the cyber attack was a “criminal act,” an official told Reuters.