Symantec shares plunge 10 percent in seconds

Shares of security software maker Symantec Corp dropped some 10 percent in a span of a few seconds on the Nasdaq on Tuesday before being halted.

The stock fell to a low of $21.93 around 10:11 a.m. EDT, with more than 500,000 shares changing hands in less than three seconds across multiple exchanges.

Equity traders called the move another single-stock "flash crash," in reference to the May 2010 selloff that saw the Dow fall more than 600 points in a matter of minutes. The dominance of high-speed trading has been a point of contention for many traders who believe it exaggerates violent moves in equities.

"Pre-HFT dominance, even back in 2003, a series of market makers would have filled this mistake with substantially less carnage," said Sal Arnuk, co-manager of trading at Themis Trading in Chatham, New Jersey.

"Today's market structure is perfectly set up to take advantage of any and all missteps in the most efficient manner ... If you were day-trading this, or had a stop-loss order in, then you got hit not because of your thesis, but because of a market structure issue."

The stock resumed trading five minutes later, and bounced back above $24.

Symantec spokesman Cris Paden said he could not immediately comment on the unusual movement in the stock price. A spokesman for Nasdaq said the exchange had no immediate comment on the trading.

(Reporting by Sruthi Ramakrishnan in Bangalore, Ryan Vlastelica in New York and Jim Finkle in Boston; Editing by Rodney Joyce, David Gaffen and Maureen Bavdek)