Websites of the UK government and several international media houses, including CNN, The Guardian, and the Financial Times, were down on Tuesday in a major internet outage. A day later, it was revealed that the outage was caused by a “customer configuration change”, which triggered a “bug” in a key delivery network. 

Nick Rockwell of US-based tech firm Fastly said in a blog post that the outage was “broad and severe” after the glitch resulting from “a valid customer configuration change.”

The outage highlighted the dependence of much of the global internet on a handful of “content delivery networks” which help speed up websites.

Rockwell said a Fastly software update from last month contained “a bug that could be triggered by a specific customer configuration under specific circumstances.”

This happened on Tuesday when “a customer pushed a valid configuration change that included the specific circumstances that triggered the bug.”

He added that the disruption was detected within a minute but that it took some 49 minutes to restore most of the impacted sites.

US-based Fastly is one of a handful of tech firms including rivals Cloudflare and Akamai which handle a large chunk of internet traffic and could be seen as chokepoints for the web.

“We are conducting a complete post mortem of the processes and practices we followed during this incident,” Rockwell said.