A technical glitch caused NYSE Euronext to release incorrect price information on more than 1,000 stocks and other securities late Thursday.
The error resulted in some online sites showing closing prices for some securities that were actually based on trades that had occurred in electronic trading after markets had closed.
The problem started at 7:27 p.m. Thursday when NYSE's Arca platform sent incorrectly coded share price information.
An e-mail sent to traders on Friday said the problem involved prices from aftermarket trades on Thursday that were incorrectly coded as if they had happened during regular trading that day. The e-mail says the mix-up affected the closing price in some shares that trade on the New York Stock Exchange as well as its Arca platform.
The mix-up confused some investors. The share price for Precision Castparts Corp. showed a decline of as much as 9.6 percent on Friday, but that was based on an incorrect comparison to the after-hours price. In reality, its shares were down less than 3 percent from Thursday's close.
"`Not fun' would be a good description of my entire morning," the company's communications director, Dwight E. Weber, said.
The error affected 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.
NYSE spokesman Rich Adamonis said more than 1,000 ticker symbols were effected. He said the mix-up is still being investigated.
In the case of Precision Castparts, the erroneous price showed up as an artificially high closing trade _ exaggerating the shares' decline on Friday. On Friday it closed at $161.92, down 2.7 percent from their correct Thursday close of $166.48.
Some websites were still showing the wrong Thursday closing price for Precision Castparts on Friday afternoon. Adonis said websites have to manually update their databases with the corrected closing prices.
About 8,000 issues trade on NYSE Euronext stock exchanges, according to the company.
The foul-up didn't have much effect on professional traders.
"As somebody who trades on the floor for a living, it hasn't generated much attention," said Gordon Charlot, managing director at Rosenblatt Securities, from the floor of the New York Stock Exchange.
AP Business Writer Matthew Craft in New York contributed to this report.