On Tuesday a number of high profile sites went down including the Guardian and New York Times, as well as British government sites, Reddit and Amazon.com

Fastly, the company behind a major global internet outage this week, said on Wednesday the incident was caused by a bug in its software that was triggered when one of its customers changed their settings.

"This outage was broad and severe, and we're truly sorry for the impact to our customers and everyone who relies on them", the company said in a blog post authored by Nick Rockwell, its senior engineering and infrastructure executive.

Fastly operates a group of servers strategically placed around the world to help customers move and store content close to their end-users quickly and safely.

Fastly said the bug was in a software update shipped to customers on May 12 but was not triggered until one unidentified customer carried out settings changes that triggered the problem "which caused 85 percent of our network to return errors".

Fastly noticed the outage within a minute it occurring at 0947 GMT, and engineers worked out the cause at 1027 GMT. Once they disabled the settings that triggered the problem, most of the company's network quickly recovered.

That meant the internet was out for about 49 minutes, fully recovered at 1235 GMT and it began rolling out a permanent software fix at 1725 GMT.

But the underlying issue of concern is how dependent the Internet is on a handful of companies and how easy it is to take out, given that resilience was what it was designed for.