U.S.-based stock-exchange operator BATS Global Markets said a system error led to hundreds of thousands of transactions being executed at prices that were not the best available.
The error dating back to 2008 caused some short-sale orders to be executed at prices that were equal to or less than the national best bid or offer price (NBBO), the company said in a statement on its website Wednesday.
Exchanges and broker dealers are required to execute transactions at the best price available, under the regulation also known as NBBO.
BATS said it was working to correct the error by Jan. 25.
Representatives from BATS and the U.S. Securities and Exchange Commission were not immediately available for comment.