呵呵，美股狂跌初步消息出来了

Market Watch的消息。应该还是自动交易软件惹的货。除了PG还有一个3M。最开始起因是某个大公司想卖16Million的EMinis，不小心打成了16Billion。

By Kristina Peterson

NEW YORK (MarketWatch) -- The U.S. stock market's rapid freefall Thursday afternoon was
accelerated by program trading, which was triggered after a sharp drop in sharp drop in shares of Procter & Gamble (PG 60.51, -0.25, -0.41%) and at least one other Dow stock, 3M Co. /quotes/comstock/13*!mmm/quotes/nls/mmm (MMM 84.25, +0.00, +0.01%) , market watchers said.

Shares of Procter & Gamble plunged to $39.37 from around $60. The New York Stock Exchange said
each stock has its own circuit breaker level. When these stocks fall below their levels, then they can be
traded on any other exchange or platform at any price. When P&G fell below its circuit breaker, a bid
came in for the stock at $39.37 from the Nasdaq, the NYSE said.

"You don't see a blue-chip stock like this go down 20 points with no news, said Frank Ingarra,
co-portfolio manager at Hennessy Funds, a quantitative firm that deals with program traders. "All of the
algorithms kicked in from this errant thing."

The Big Board also noted that 3M fell below its circuit-breaker level.

Several market watchers said they heard a major firm may have accidentally released an errant program,
where a trader accidentaly placed an order to sell $16 billion, instead of $16 million, worth of e-minis,
the futures contracts tied to equity indexes.

E-minis are traded at the Chicago Mercantile Exchange. Allan Schoenberg, a spokesman for CME
Group, said the exchange was examining trades.

"Whenever the market moves up or down like the swings we saw today, we take a look to make sure
everything's operating properly. That's exactly what we're doing now," Schoenberg said. "If the exchange finds anything amiss, it would report its finding on its website."

Traders also also noticed errant trades among exchange-traded funds, including the iShares Russell
1000 Value Index Fund (IWD), which dropped from close to $60.00 to 7.5 cents.

"These ETFs traded to lows that are not mathematically correct," he said.

(Erik Holm contributed to this story.)