The NY Times as a great article about the role of high frequency traders in the financial market, and how they gain at a loss to others.

It was July 15, and Intel, the computer chip giant, had reporting robust earnings the night before. Some investors, smelling opportunity, set out to buy shares in the semiconductor company Broadcom. (Their activities were described by an investor at a major Wall Street firm who spoke on the condition of anonymity to protect his job.) The slower traders faced a quandary: If they sought to buy a large number of shares at once, they would tip their hand and risk driving up Broadcom’s price. So, as is often the case on Wall Street, they divided their orders into dozens of small batches, hoping to cover their tracks. One second after the market opened, shares of Broadcom started changing hands at $26.20.

The slower traders began issuing buy orders. But rather than being shown to all potential sellers at the same time, some of those orders were most likely routed to a collection of high-frequency traders for just 30 milliseconds — 0.03 seconds — in what are known as flash orders. While markets are supposed to ensure transparency by showing orders to everyone simultaneously, a loophole in regulations allows marketplaces like Nasdaq to show traders some orders ahead of everyone else in exchange for a fee....

Soon, thousands of orders began flooding the markets as high-frequency software went into high gear. Automatic programs began issuing and canceling tiny orders within milliseconds to determine how much the slower traders were willing to pay. The high-frequency computers quickly determined that some investors’ upper limit was $26.40. The price shot to $26.39, and high-frequency programs began offering to sell hundreds of thousands of shares.

The result is that the slower-moving investors paid $1.4 million for about 56,000 shares, or $7,800 more than if they had been able to move as quickly as the high-frequency traders.

So basically Goldman Sachs is able to see orders before they are executed, and know in advance when orders will come in. So they buy the stock, driving up the price, and sell it back to the slower traders at a higher price. No need to have a genuine insight into a company's true value, just a brief moment of arbitrage.

It seems like this whole scheme is dangerously close to insider trading. After all the reason why we have laws against insider trading is to limit the effect of information asymmetries. Much of Goldman Sach's profit seems to be based in using inside knowledge to take money from other investors.

Heads they win, tails you lose.

It's a magnificent system, huh?