A previous version of this report misstated the title of the book. The error has been corrected.

WASHINGTON (MarketWatch)–A former banker-turned-blogger has written a book to help people understand the complex world of high-frequency trading and dark pools.

“Dark Pools & High Frequency Trading for Dummies,” which was made available was written by Jay Vaananen, who worked for many years in private banking in Luxembourg before starting the blog Banker’s Umbrella.

Vaananen, who lives in Finland, said John Wiley & Sons which publishes the popular “For Dummies,” series, contacted him to write a book about dark pools, which are private trading venues.

“I said if you are doing a dummies book, you can’t handle dark pools without high-frequency trading because dark pools came about because of HFT,” Vaananen said.

Vaananen said he first began starting to notice problems while working in banking with high-frequency trading.

“You’d hit the bid, and all of a sudden it would slide and you’d get a worse price,” he said. “You could see this kind of system doing the orders automatically.”

But Vaananen said it is difficult to explain much of high-frequency trading because it is not a single thing but has numerous different aspects that sometimes are independent of each other.

“What worries me is the whole complexity, because there’s no way a person’s brain capacity can manage the whole complexity of the system,” he said. “And it’s all happening in milliseconds.”

His main concern with high-frequency trading is what will happen when something goes wrong and that it will go wrong quickly.

“It is a big, big risk, and you don’t know where the risk is going to come from, and how it’s going to crash,” he said.

He also said he is worried about activity occurring in dark pools. He said it is possible to manipulate the spread by taking it through a dark pool, which can affect the prices on lighted exchanges and can compromise market integrity.

“Us bankers, we’re not that trusted anyway,” he said. “We need lots of players on the market and we have less and less.”

Vaananen left his job in banking and said he plans to continue writing on issues related to banking and high-frequency trading

“Everything related to equity markets rely on what’s happening with HFT,” he said. “If you want to operate in the market, you have to know what’s going on.”

