Major internet services including Twitter and Spotify suffered outages today as a US internet provider came under cyber attack.

The internet service company Dyn said it had suffered a denial of service (DDoS) attack on its domain name service shortly after 12pm Irish time, but that services had been restored in about two hours.

Other affected sites, which serve millions of customers, reportedly included the crafts marketplace Etsy and the software developer site Github, according to the website Hacker News.

"This morning, October 21, Dyn received a global DDoS attack on our Managed DNS infrastructure in the east coast of the United States," Executive Vice President for products at Dyn Scott Hilton said in a statement.

"DNS traffic resolved from east coast name server locations are experiencing a service degradation or intermittent interruption during this time," Mr Hilton added.

"We have been aggressively mitigating the DDoS attack against our infrastructure."

The company said it was continuing to investigate.

Distributed denial of service or DDoS attacks involve sending high volumes of requests to websites which can be taken off line as a result.

Domain Name Services are a crucial element of internet infrastructure, converting numbered Internet Protocol addresses into the domain names that allow users to connect to internet sites.