Stock Swing Still Baffles, With an Ominous Tone, by Graham Bowley. The New York Times, 22 August 2010.
The stock market mysteriously plunges 600 points — and then, more mysteriously, recovers within minutes. Over the next few weeks, analysts at Nanex, an obscure data company in the suburbs of Chicago, examine trading charts from the day and are stunned to find some oddly compelling shapes and patterns in the data.

To the Nanex analysts, these are crop circles of the financial kind, containing clues to the mystery of what happened in the markets on May 6 and what might have caused the still-unexplained flash crash.

The charts — which are visual representations of bid prices, ask prices, order sizes and other trading activity — are inspiring many theories on Wall Street, some of them based on hard-nosed financial analysis and others of the black-helicopter variety.

To some people, like Eric Scott Hunsader, the founder of Nanex, they suggest that the specialized computers responsible for so much of today’s stock trading simply overloaded the exchanges.
Could a foreign power or non-state actor “weaponize” High-Frequency Trading? Have they already?