Trades in about 1,600

Nasdaq

-listed stocks were canceled Friday morning after regulators discovered pricing errors generated by a member firm's computer system.

The trades, most in thinly traded issues, occurred over a 20-minute period just prior to and just after the 9:30 a.m. EDT open, starting at 9:19 a.m. The stocks were bought and sold on electronic crossing networks that match buyers and sellers both during and outside of regular market hours.

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A list of the securities involved was compiled by the market and can be downloaded from the

Nasdaq's Web site.

According to a release, the problem involved trades that occurred at prices that were too far above or below the previous price. Trades in the named stocks that occurred at prices more than 15% above or below the prior day's close -- unless the moves were justified by news -- will be canceled, the Nasdaq said.

The trades were reviewed according to Nasdaq rule 11890, which allows the market regulator to cancel trades that were "clearly erroneous."