Popular websites such as Twitter, Spotify, Reddit, SoundCloud, PayPal, Netflix and several others remained unreachable for part of the day after being hit by three web attacks on Friday (October 21).
Access to sites such as Etsy, the New York Times, Pinterest, Github and Tumblr as well as some cable firms, was also reported as being intermittent.
All the firms are customers of a web technology provider called Dynamic Network Services Inc. or commonly known as Dyn, which they use to help users find their sites online.
The FBI and Department of Homeland Security are investigating the disruption which affected many users in the U.S across the East coast for two hours starting from 7:10 a.m. EDT.
Dyn, Inc., a firm that provides some hosting services for the internet's Domain Name System (DNS), posted online that its engineers are working to "mitigate several attacks" aimed at their DNS infrastructure.
The firm said that the first attack was a distributed denial of service (DDoS) attack, which overwhelms its target with traffic until it's paralyzed.
It is not yet clear who is behind the attack and what was the motive.
Chief Strategy Officer at Dyn, Kyle York, told ABC News that this DDoS attack was sophisticated and complex than the general ones and appears to have a large botnet or network of botnets to be involved in it.
The incidents mark a change in tactics as DDoS attacks which are more typically aimed at a single site.
