Econintersect: There may be risks of high speed trading (HST - aka high-frequency trading) other than market manipulation. HST uses of sophisticated technological tools / computer algorithms to quickly move in and out of market position. Trading speeds have increased from seconds to milliseconds (thousandth of a second) to microseconds (millionth of a second) and are migrating to nanoseconds (billionth of a second). Concerns include the risks to the markets due to the rate large unintended postions can accumulate - as well as feedback loops where a cascade of different HST computers start reacting to movements.
A Chicago Fed study looks at HST and offers several public policy questions for consideration.