Stock in the parent of United Airlines sank from nearly $12.50 a share to $3, before trading was halted, after Google's news service surfaced an apparently new story about a bankrutcy filing by the airline. Google's search engine picked up the story from a new link on the website of a South Florida newspaper. The underlying article, published by the Chicago Tribune in December 2002, did not carry a date.
According to the Wall St. Journal,
"The damage was exacerbated by the growing use on Wall Street of automated programs that trigger stock trades without any human interaction. The so-called algorithmic trading mechanisms, which buy and sell stocks based on news headlines and earnings data, were responsible for roughly a quarter of New York Stock Exchange trades in the last week of August.
Investors said simple human scrutiny would have indicated the UAL story was old, but computerized trading systems don't make such determinations."
See, "UAL Story Blame Is Placed on Computer," Sept. 10, 2008, at http://online.wsj.com/article/SB122100794359017593.html?mod=todays_us_marketplace.