Three successive cyber attacks left many websites down or disrupted for internet users on Friday. The Eastern United States felt the biggest impact, but issues accessing certain sites were reported globally. The target of the attacks was Dyn, one of the world's largest internet service providers, responsible for managing domain name servers for many major corporations including Netflix and Twitter.

The DDoS attack mainly affected clients of Dyn, overloading sites with web traffic by sending them “more than 150,000 requests for information per second,” according to NBC News. Servers became overwhelmed with data and were unable to process the incoming connections, causing them to slow down or in some cases shut down completely. Gizmodo reported problems for a number of major sites including Twitter, Reddit, Pinterest, Paypal, Grubhub, Etsy, and Yelp, as well as news outlets like CNN and the New York Times, in addition to popular streaming sites like Netflix, HBO Now, iHeartRadio, Spotify, and Soundcloud.

Dyn provided this update on their website immediately after the first attack:

“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.”

Around 9 a.m. Eastern time, Dyn reported that service had been restored. Three hours later, however, another attack was launched against the Dyn servers, leading to this update at about 2 in the afternoon:

“Our engineers continue to investigate and mitigate several attacks aimed against the Dyn Managed DNS infrastructure.”

Then again at 4 p.m., Dyn was assaulted with another DDoS. Company engineers investigated the outages and were quickly able to restore the servers; however, they were unable to determine who committed the act of cyber vandalism.

At this time much remains unknown about the attacks—most importantly who committed them and the extent of the damage. But one thing is for certain, at a time when over three billion people throughout the world use and depend on the internet, the fact that hackers successfully disrupted service for major websites not once, not twice, but three times in one day is deeply concerning.