WASHINGTON—An unregulated cryptocurrency exchange whose employees said they wanted to be aggressive about trading digital assets, even though their legal status was uncertain, has agreed to pay $10 million to settle a regulatory investigation.

Poloniex LLC violated investor-protection laws by not registering its operations with federal regulators, the Securities and Exchange Commission said Monday. The Boston-based company allowed users to trade digital assets that were unregistered securities from 2017 through 2019, the SEC alleged.

Poloniex agreed to settle the SEC’s investigation without admitting or denying the claims. An attorney for the company and a spokesman for the firm that previously owned it, Circle Internet Financial Ltd., didn’t immediately return messages seeking comment.

The SEC has recently vowed to bring accountability to a crypto sector that Chairman Gary Gensler this month called the “Wild West.” Mr. Gensler said last week that crypto exchanges should consult with the SEC about whether the assets they trade qualify as securities, and therefore should be registered with the market regulator.

The start of the SEC’s investigation of Poloniex predated Mr. Gensler’s remarks. The agency’s enforcement investigations typically take between one and two years to complete.

“Poloniex chose increased profits over compliance with the federal securities laws by including digital asset securities on its unregistered exchange,” said Kristina Littman, chief of the SEC enforcement division’s cyber unit.

Circle sold the trading platform in 2019, losing nearly $157 million on the investment. Circle has announced it will go public in a $4.5 billion special-purpose acquisition company merger. In July, it disclosed the probable fine over the Poloniex investigation.

The SEC warned the crypto industry in 2017 that many crypto assets were likely securities and therefore should comply with investor-protection rules. Nonetheless, Poloniex employees said internally in August 2017 that they wanted to be aggressive about listing assets that might be securities to win market share, the SEC said in a settlement order.

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