Marketplace Tech is spending all week looking at the risks technology can introduce to investing. Today, part one of a look at high-frequency trading. Critics of too much high-frequency trading say it makes markets vulnerable to manipulation, and the algorithms that fuel it can cause abrupt dips and rises in stock prices. Brad Katsuyama is a former big bank trader who's the subject of the 2014 Michael Lewis book "Flash Boys." He started studying high-frequency trading before the 2008 financial crash and eventually decided to start his own stock exchange to remove the influence of trading technologies that he says rig the market. Molly Wood talks with Katsuyama and Jonathan Macey, professor of corporate law at Yale, about the implications of high-frequency trading. (09/18/18)