EXPLAINER: Just how vulnerable is the internet?

BOSTON (AP) — An outage at a little-known firm that speeds up access to websites knocked a lot of top internet destinations offline on Tuesday, disrupting business and leisure for untold millions globally. The problem was quickly resolved. The company, Fastly, blamed a configuration error in its technology.

But the incident — Fastly's traffic dropped 75% for about an hour just as the U.S. East Coast was beginning to stir —raises questions about how vulnerable the global internet is to more serious disruption.

WHAT'S A FASTLY? WHY DID ITS TECHNICAL PROBLEMS LEAD TO SO MANY OUTAGES?

San Francisco-based Fastly isn't a household name, but its “edge server” computing technology is used by many of the world's most popular websites, such as The New York Times, Shopify, the Guardian, Ticketmaster, Pinterest, Etsy, Wayfair and Stripe. The British government is among its clients.

The company provides what's called a content delivery network — an arrangement that allows customer websites to store data such as images and videos on various mirror servers across 26 countries so that the data is closer to users, and thus shows up faster. Many of Fastly's customers are news sites that use its technology to update their websites with breaking news. Buzzfeed, for example, used Fastly to cut the time its users took to reach the site by half. Fastly had $290.9 million in revenues last year.

WAS THERE ANY BACKUP? COULD OTHER COMPANIES HAVE STEPPED IN IF THE PROBLEM HAD BEEN MORE SEVERE?

Customers rely on Fastly and its rivals to host and protect their website data from denial-of-service attacks and disruption from spikes in traffic. Had this outage been more serious, customers could have moved to competitors such as Cloudflare or Akamai. But that's not simple; many businesses would have...