The Nasdaq Stock Market experienced issues processing some quotes around the closing of trading Wednesday afternoon, according to a trader notice.

Nasdaq OMX Group Inc. (NDAQ) said traders may have been looking at "stale" price quotes for some Nasdaq-listed securities in a 13-minute window bracketing the close of trading and ending around 4:12 p.m. EDT.

Nasdaq said issues processing market data prompted the stale quotes, which affected securities whose ticker symbols began with the letters S through Z.

U.S. stocks plunged on Wednesday on fears surrounding further contagion among European banks and the Federal Reserve's gloomy economic outlook. The Dow Jones Industrial Average slumped 519.83 points, adding to several days of extreme volatility.

The New York Stock Exchange put into effect its so-called "Rule 48" before Wednesday's open, the second time this week. The procedure aims to smooth the opening of trading on a session that is likely to get volatile. Read More