To crack down on confidentiality loopholes, the Securities and Exchange Commission has ordered hedge fund group D.E. Shaw & Co. to reveal its holdings, valued at $21 billion.

A top-20 U.S. hedge fund manager, New York-based D.E. Shaw has relied on an SEC loophole to keep its positions secret for at least the last five years, Bloomberg News reports. The ruling is considered a setback for D.E. Shaw because by revealing its holdings, other investors are likely to invest in them, making them less profitable. The ruling may also give competitors insight into the strategies and computer models developed under the fund's founder, David Shaw, which include taking advantage of anomalies in stock prices.

SEC regulations require firms with $100 million or more of equity under management to list their stock holdings at the end of every quarter in a form that is available to the public.

The SEC revoked the firm's confidential status on Dec. 13. Neither party would comment on the action, Bloomberg said.

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