I very much appreciate your concerns about high-frequency trading (HFT) on today’s stockmarkets (“Not So Fast,” August 6, 2011). As you say, it is accelerating all the time. Trades can be made in ever-smaller fractions of a second. Also, HFT represents an ever-larger portion of trading. Now it accounts for up to three-quarters of all Wall Street volume, and it is bound to grow. The thoughtful investor concerned with the efficient allocation of capital is rapidly disappearing. All HFT does is spotting and acting on market prices sooner than competitors. It is a mindless game. The “flash crash” of May 2010 thus looms ever more ominously. Although it was quickly righted, such a crash would be impossible to right in a situation we have at the moment, when stockmarkets are plummeting amid high volatility. A flash crash at times like this would make all prices completely meaningless. Coupled with “spoof” orders you mention, which involve deliberate HFT manipulation of the market, this also means that stockmarkets can be driven to debacle on purpose. A couple of clever hacks can bring the whole system down in a jiffy. What is the likelihood of such a diversion? It is anyone’s guess, of course.