Flash Boys

In July 2009, FBI agents arrested Sergey Aleynikov at Newark Liberty International Airport. He was a programmer who had just left his job at Goldman Sachs. The charge: stealing proprietary computer code. But here's what made the case strange. No one could explain what the code actually did. The FBI agent who interrogated Aleynikov had been a stock trader. He didn't understand the technology. The prosecutors couldn't explain it to the jury. Even Goldman Sachs executives seemed fuzzy on the details.

What they kept calling him was a "high frequency trading programmer." That phrase meant almost nothing to the public. It meant almost nothing to the court. But it meant everything to Michael Lewis, the author of this book. He had spent decades writing about Wall Street's inner workings. He knew that when a giant bank like Goldman Sachs sends the FBI after a single programmer, something important is being hidden.

The arrest opened a door into a world most people didn't know existed. The US stock market had transformed completely. Gone were the shouting traders on the floor of the New York Stock Exchange. Gone were the paper tickets and hand signals. In their place sat black boxes in New Jersey and Chicago. Computers traded with other computers. Algorithms made decisions in microseconds. The ticker tape running across cable news screens captured almost nothing of what actually happened.

What was really happening was this: a new kind of predator had emerged. High-frequency traders, or HFTs, had built computers so fast they could detect other people's trades before those trades could be completed. They could buy stocks milliseconds ahead of ordinary investors, then sell them back at a slightly higher price. The margins were tiny. But they did this millions of times a day. The profits ran into the billions.

The system had become rigged. Not by conspiracy. Not by evil villains. But by the simple physics of speed. If you could send your signal a few milliseconds faster than everyone else, you could see their intentions before they acted. You could front-run them. You could pick them off. And because the market had fragmented into dozens of different exchanges, all connected by fiber-optic cables of varying lengths, there were endless opportunities to exploit these tiny time gaps.

This is where the book's hero enters. Brad Katsuyama was a Canadian trader at the Royal Bank of Canada. He was unfailingly polite, almost to a fault. His colleagues called it "RBC nice." But in 2006, he noticed something disturbing. Every time he tried to buy a stock, the price jumped. Not by much. Not slowly. Instantly. It was as if someone knew what he was about to do and moved the price against him.

He spent months testing theories. He built a program called THOR that deliberately slowed his orders so they reached all exchanges at the same time. It worked. The price manipulation stopped. Katsuyama had discovered that HFTs were using speed to detect his trades. But this discovery led to a harder question: what could anyone do about it?

The answer, Katsuyama decided, was to build a new stock exchange. One designed from the ground up to be fair. One that neutralized the speed advantage. He called it the Investors' Exchange, or IEX. And he recruited a team of misfits to build it: puzzle champions, telecom experts, Wall Street veterans who had seen too much corruption to stay silent.

But the system they were fighting didn't want to be fixed. The big banks made money from the speed advantage. The exchanges made money from the complexity. And the HFTs made billions from the loopholes. When Katsuyama's team tried to expose the problem, they faced sabotage. Banks sent tiny orders to IEX to scare away investors. Rumors spread that the exchange was corrupt. The SEC defended HFT as a natural evolution of the market.

This brings us back to Sergey Aleynikov. He was a brilliant Russian programmer who had helped build Goldman Sachs' HFT system. He was also a victim of the very system he helped create. When he left Goldman for a smaller firm where he could do more creative work, he emailed himself some code. Some of it was open-source code he had modified. Some was proprietary. This was standard practice in the industry. But Goldman Sachs called the FBI.

The arrest was dramatic. The trial was a farce. The jury didn't understand the technology. The only expert witness was a finance professor with no direct knowledge of HFT. Aleynikov was convicted and sentenced to eight years in prison. He lost his marriage. He lost his career. And when Lewis assembled a jury of actual HFT experts to review the case, they concluded that what Aleynikov had taken was essentially worthless outside Goldman's system. The real crime, they suggested, was that Goldman wanted to hide how weak their HFT capabilities actually were.

So here is the puzzle at the heart of this book. The stock market is rigged. A small group of insiders is fighting to reform it. But the same forces that rigged the market also control the legal system, the regulators, and the flow of information. The same bank that destroyed one programmer's life would later save IEX from collapse—not out of morality, but out of self-interest.

What does it mean to fight a system that rewards corruption? What does it take to build something fair when everyone around you profits from unfairness? And what happens to the people who try?