Exchanges began embracing electronic trading about three decades ago. Electronic trading enabled some companies to use market-moving information milliseconds before their competitors, sparking a technological arms race.

Over the past 15 years, meanwhile, the global financial market has fragmented: Where there were once three main U.S. exchanges, there are now more than 40 exchanges and alternative trading systems.

And high-frequency trading companies have largely replaced traditional broker-dealers, using algorithms instead of human traders to make decisions in milliseconds, mostly in response to orders made by other algorithms.

Technology has made trading faster and more efficient. But the system is also more opaque, and some wonder whether high-frequency trading companies are profiting at the expense of institutional and retail investors.

“There are probably about 5,000 people who know how the trading system works but none of them will speak about the way these high-frequency firms make money,” said a financial industry insider, who spoke on the condition they not be named because their employer had not authorized them to discuss the matter publicly.

On May 6, 2010, the Dow Jones Industrial Average plummeted nearly 1,000 points, then its biggest intraday point drop ever. A government investigation blamed a big order that triggered a selloff for the “Flash Crash,” but couldn’t identify the structural problem that led to markets plunging 10% in 20 minutes before rising again.

Hunsader’s research, published that June, suggested that high-frequency trading companies responded to the first big order by flooding the market with orders that were withdrawn before they were filled, overwhelming the central feed of pricing information other investors needed to complete trades.

The practice, Hunsader says, created illusory liquidity that led to the “Flash Crash” and other dramatic market events that followed. (He coined the term “quote stuffing” to describe it.) “It was a bit like a denial-of-service attack on a website,” said Hunsader. “The system can’t handle it and crashes.”

Hunsader, sure he’d identified a core structural issue, later published more than 2,000 more reports — some a few sentences, others more detailed explanations of how he says markets are manipulated.

“I peeked behind the curtains and did not like what I saw,” said Hunsader.

In the reports, and on social media, he criticizes high-frequency traders, which he says use technology to break Securities and Exchange Commission trading rules; exchanges, which he says benefit from immunity from prosecution and turn a blind eye to wrongdoing; and regulators, who he says don’t do enough to protect investors.

David Fuller's view

For a number of years high-frequency trading firms have been operating computer driven, predatory, front-running systems which should be illegal but too often are not.  This tells us that many of our market officials and regulators are amoral at best.