Computer problems at the Nasdaq Stock Market led to erroneous stock quotes on a number of major online financial news sites and brokerages Thursday and prevented approximately 81,000 trades from being reported in the last minutes of the previous trading session.

The stocks affected are all listed on the New York Stock Exchange. NYSE-listed stocks can also be traded electronically on Nasdaq's computer platform, and Nasdaq is responsible for reporting those trades to a consolidated listing service so investors can see the latest price for a given stock, whether it was traded on the floor of the NYSE or via Nasdaq's computers.

The Nasdaq said a computer glitch occurred at approximately 5:50 p.m. Eastern time Wednesday, when 610 transactions involving NYSE-listed stocks that had been made at 9:50 a.m. were reposted to the consolidated tape. That resulted in erroneous closing prices for a number of NYSE-listed stocks being reported, according to a notice issued by Nasdaq Operations late Wednesday.

It was not immediately known how many NYSE-listed stocks were affected by the computer errors.

A number of Web sites viewed by The Associated Press Thursday — including MSN Money, Yahoo! Finance and BigCharts.com, along with online brokers Charles Schwab and E-Trade — showed erroneous price changes for a handful of NYSE stocks. Stock quote services on both NYSE.com and Nasdaq.com also posted incorrect price changes.

AMR Corp., for example, actually closed at $20.39 on Wednesday, but the retransmitted trades from earlier in the session had AMR closing at $18.79. In midmorning trading on Thursday, AMR was actually down 16 cents at $20.23, yet other sites listed that quote as being up $1.44 to $20.23.

The Associated Press' market data services caught the errors, and the stock tables it sent to newspapers were correct.

Earlier Wednesday, a related computer problem resulted in the 81,000 trade reports from being sent to the consolidated tape in the last 20 minutes of trading. The trades themselves were executed, but the price quotes from those trades could not be seen by traders on the NYSE or on non-Nasdaq computer trading systems.

The Nasdaq only trades a small percentage of NYSE-listed stocks on a given day. However, it's important for traders to know the most recent price a stock has fetched to help determine whether to buy or sell, and the absence of those Nasdaq trades in the last 20 minutes of trading resulted in investors not having a complete picture of the market as they made their trading decisions.

A spokeswoman for the Nasdaq had no immediate comment beyond the Nasdaq Operations notice sent Wednesday night. A spokesman for the NYSE had no immediate comment.