It’s fast and furious, and highly controversial. High-frequency trading is the computer–based buying and selling of shares within fractions of a milli-second. A new study just out in Britain suggests this kind of trading is mostly beneficial.
The markets tumbled Friday, but the declines were nothing compared to the Black Monday crash of Oct. 19, 1987. The Dow Jones shed 22 percent -- the equivalent of a 3,000-point drop today.