Another reform made was the "Small-order execution system", or "SOES", which required market makers to buy or sell, immediately, small orders (up to 1,000 shares) at the market maker's listed bid or ask. The design of the system gave rise to arbitrage by a small group of traders known as the "SOES bandits", who made sizable profits buying and selling small orders to market makers by anticipating price moves before they were reflected in the published inside bid/ask prices. The SOES system ultimately led to trading facilitated by software instead of market makers via ECNs.
