NYSE Euronext says it sent out incorrect price information on more than 1,000 stocks and other securities, causing some shares to show price swings that hadn't really happened.
NYSE spokesman Rich Adamonis says the mix-up is still being investigated.
An email sent to traders says the problem involved prices from aftermarket trades on Thursday that were incorrectly coded as if they had happened during regular trading that day. The email says the mixup potentially affected the closing price in some shares that trade on the New York Stock Exchange as well as its Arca platform.
The impact was on some stocks, exchange-traded funds, and mutual funds that started with the letters A though T. Symbols starting with U through Z were not affected.