Washington, Oct 22: Twitter and some other major websites were shut down on the US East Coast for several hours on Friday as an American Internet service provider called Dyn and Amazon's web services unit were hit by waves of cyber attacks.
Dyn, headquartered in New Hampshire, said in posts on its website that its Domain Name System (DNS) infrastructure suffered a distributed denial-of-service (DDoS) attack starting at 7.10 a.m. EDT (4.40 p.m. Indian Standard Time), Xinhua news reported.
A DDoS attack is an attempt to make an online service unavailable by overwhelming it with traffic from multiple sources, and the company said the attack is "mainly impacting US East".
About two hours later, Dyn said "services have been restored to normal".
But it wasn't over. The company confirmed that a second DDoS attack took place at 11.52 a.m. EDT (8.30 p.m. IST).
"This DDoS attack may also be impacting Dyn Managed DNS advanced services with possible delays in monitoring," it said.
In an update posted at about 2 p.m. (11.30 p.m. IST), Dyn said its engineers "continue to investigate and mitigate several attacks aimed against the Dyn Managed DNS infrastructure".
Amazon Web Services (AWS), a unit of Amazon.com that hosts many of the web's popular destinations including Netflix, reported an attack that also affected people on the US East Coast around the same time in the morning.
"Between 4.31 a.m. and 6.10 a.m. PDT (5.00 p.m. and 6.40 p.m. IST), we experienced errors resolving the DNS hostnames used to access some AWS services in the US-EAST-1 Region," the company said on its website.
But this issue has been resolved and the service is now operating normally, it noted.
Currently, it's unknown who was behind the attacks.
White House spokesman Josh Earnest said the US Department of Homeland Security is monitoring this situation and will take a close look at it.
"But at this point, I don't have any information to share about who may be responsible for that malicious activity," Earnest told reporters.