What made a six-year-old article about a bankruptcy filing by United Airlines reappear on Wall Street traders’ screens on Monday as if it were fresh news, prompting a sell-off that erased $1 billion in the company’s market value in a matter of minutes? The path the article followed from forgotten archive entry to present-day stock-killer has begun to emerge, and it raises some interesting questions about how news rockets around the Web.

Both human error and far-from-foolproof technology seem to have played a role in the episode, which involved a 2002 Chicago Tribune report; the web site of the Sun Sentinel, a Florida newspaper owned by the same company; the Bloomberg News financial wire service; and Google, all apparently unwittingly.