LONDON—Fastly, the company hit by a major outage that caused many of the world’s top websites to go offline briefly this week, blamed the problem on a software bug that was triggered when a customer changed a setting. The problem at Fastly meant internet users couldn’t connect to a host of popular websites early Tuesday including The New York Times, the Guardian, Twitch, Reddit and the British government’s homepage. “We experienced a global outage due to an undiscovered software bug that surfaced on June 8 when it was triggered by a valid customer configuration change,” Nick Rockwell, Fastly’s senior vice president of engineering and infrastructure, said in a blog post late Tuesday. He said the outage was “broad and severe” but the company quickly identified, isolated and disabled the problem and after 49 minutes, most of its network was up and running again. The bug had been included in a …