The stock market plunged Thursday in a five-minute selloff that appeared to be triggered by a breakdown of trading systems.
After dropping nearly 1,000 points, the market rebounded but still closed down 3.2 percent, leaving Wall Street struggling to determine what happened, according to an article in The Wall Street Journal.
The Dow Jones Industrial Average closed at 10,520 Thursday, though it dropped below 10,000 in afternoon trading. The 52-week high and low are 11,309 and 8,058.
The market opened this morning at 10,519, but dropped about 200 points in mid-morning trading.
Investors already were jittery about the ripple effects of the crisis in Greece when the market went into free fall at 2:42 p.m. By 2:47, the Dow had dropped below 10,000 in the biggest intraday point drop in its history.
By 3:07, the market had regained 500 points, ultimately staggering to close down 347.8 points.
The Securities and Exchange Commission and the Commodity Futures Trading Commission said they were working with other regulators to review "unusual trading activity," according to the article.
The major U.S. stock exchanges said they were looking for trading glitches and examining potentially erroneous trades in multiple stocks. Major exchanges said they will cancel erroneous trades that occurred during the selloff.
Multiple stocks, from Accenture PLC to Boston Beer Co., momentarily lost nearly 100 percent of their value, changing hands for just one penny. Exchange-traded funds, which are index funds that trade like stocks on exchanges, were also temporarily vaporized.
The market was already down some 500 points when the selloff began.
Traders immediately said a market glitch must have contributed to the decline. They theorized that high-frequency trading firms, which use computer programs to trade and account for about two-thirds of the market's overall volume, might have contributed to the speed of the decline, although they offered no specifics.