How vulnerable is the internet?

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.