A trader watches the numbers in the S&P 500 pit at the CBOE on May 6 during the Dow's 1,000-point freefall. Stocks recovered, finishing down about 3 percent. (Terrence Antonio James/Chicago Tribune)

Regulators are scrutinizing what some in the stock market are calling “quote stuffing,” trading in which unusually large numbers of orders to buy or sell stocks are placed in a fraction of a second, only to be canceled almost immediately.

The Securities and Exchange Commission has begun looking into whether the practice is putting some investors at a disadvantage by distorting stock prices, according to people familiar with the matter. The SEC is looking at what role, if any, quote stuffing played in the May 6 “flash crash,” when the Dow Jones Industrial Average collapsed 700 points in minutes, the people say. Get the full story »