Three cryptocurrency exchanges may be operating illegally in New York, according to the state’s legal chief.

In a report Tuesday, Attorney General Barbara Underwood said her office referred Binance, Kraken and Gate.io to the New York Department of Financial Services for possible violation of digital-currency regulations. Each of those exchanges had earlier refused to provide information requested by the state. The three firms didn’t immediately respond to requests for comment.

“New Yorkers deserve basic transparency and accountability when they invest – whether on the New York Stock Exchange or on a cryptocurrency platform,” Underwood said in a statement. “Many virtual currency platforms lack the necessary policies and procedures to ensure the fairness, integrity, and security of their exchanges.”

In April, the attorney general began asking 13 major crypto marketplaces for details on their operations, internal controls, and safeguards against market manipulation and fraud. Nine of the platforms participated, while the other four claimed they don’t allow trading in New York. Kraken Chief Executive Officer Jesse Powell in April dismissed the office’s request in a tweet.

Binance is the world’s largest crypto exchange by trading volume, according to data compiled by CoinMarketCap.com. Kraken is ranked as the 14th biggest and Gate.io is the 27th.

The report found three “areas of concern” in the crypto markets, specifically flagging lack of protection from abusive trading practices, conflicts of interest and limited safeguarding of customer funds.

“Virtual asset trading platforms have yet to implement serious efforts to monitor and stop abusive or manipulative trading,” Underwood said. “Few platforms seriously restrict, or even monitor, the operation of ‘bots’ or automated algorithmic trading on their venue.”

Prop Trading

The attorney general also noted that some exchanges engage in proprietary trading, meaning they trade on their own platforms on behalf of themselves. Nearly 20 percent of executed volume on San Francisco-based Coinbase Inc.’s marketplace, for example, came from its own trading, according to the report.

Coinbase says on its website that it trades its own corporate funds on its platform. A spokesman didn’t immediately have a comment Tuesday. Coinbase Pro is the 16th-largest exchange, according to CoinMarketCap.com.

“Such high levels of proprietary trading raise serious questions about the risks customers face on those platforms,” the report said. “As a general principle, when a significant percentage of the volume in one or more assets on a venue is attributable to one source, customers face the risk that the availability of liquidity in those assets could change, without notice and at any time.”

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