While news producers scramble to put together a segment explaining today’s stock market crash, they will inevitably try to tie it to larger unrest. And there’s a lot to choose from: the unrest and instability in Greece, the Gulf oil spill, and maybe even the immigration law in Arizona deserve quality reportage. But according to Matt Nesto’s reporting on CNBC, the real reason behind the sudden and severe dip in the Dow Index might have been a typo. 
 
 According to some, the market crash (that at one point saw the Dow Index fall as much 10%) may have been sparked by a sudden and significant sell in shares of Procter and Gamble. Nesto reports that, according to multiple sources, somebody hit a “B” instead of an “M” on the keyboard, selling a billion shares rather than a million. Huh. Nesto’s report follows: 
 
 You see that below me that it says that trading error at a major firm. We’ve got multiple sources saying that that major firm that reportedly made the trading error is Citigroup. We’ve of course been in touch with Citigroup and they say they have no evidence of a bad trade but they are investigation the situation. I would just repeat that we have had more than one source pointing to Citigroup as the firm that did or issue the errant trade we’ve talked about the b entered vs the m the billion versus the million. 
 
 There are a million reasons why a market behaves one way or another, and according to CNBC, Citigroup maintains that they have not uncovered an irregularities in their orders. Investigations behind the sudden crash (which rebounded to a loss of only 3%) will continue, and some are positing a more mysterious “computer glitch.” 
 
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 Update: According to CNN Radio reporter Lisa Desjardins, the tech error in question may have been on NASDAQ’s end. 
 
 
 
 
 
 
 
 
 
 For a more complete analysis, check out Geekosystem’s rundown: ||||| WASHINGTON (MarketWatch) -- Two top financial regulators said Tuesday they aren't sure yet what caused the stock market's dizzying May 6 plunge and partial recovery, but they don't believe any one event created it. 
 
 At issue is the Dow Jones Industrial Average drop of nearly 1,000 points last Thursday - a fall of roughly $1 trillion in market value -- much of it in a matter of minutes, before recovering to a 348-point loss for the session. 
 
 Both Mary Schapiro, Securities and Exchange Commission chairwoman, and Gary Gensler, Commodity Futures Trading Commission chairman, refuted speculation that a trader might have made a so-called "fat finger" error that contributed to the stock market plunge. 
 
 "Neither our review nor reviews by the relevant exchanges and market participants have uncovered such an error [fat-finger] trade," said Schapiro at a Capitol Hill hearing on the stock plunge and a subsequent investigations into the matter by the SEC and Commodity Futures Trading Commission. 
 
 The two agencies plan to provide preliminary findings on what caused the stock plunge next week. 
 
 Some observers have speculated that a "fat finger" error may have taken place, in which a trader enters an order for billions of shares rather than an intended order for millions. Gensler also said Tuesday in testimony that the agency's staff review "produced no evidence" indicating that a "fat finger" was the catalyst. 
 
 The SEC and the CFTC have reached a preliminary agreement with securities exchanges to create a unified stock-by-stock circuit breaker for all exchanges -- including electronic exchanges -- to halt trades or slow down the pace of trading during a massive market downturn, according to people familiar with the discussions. Read about preliminary agreement. 
 
 "With our children, we tell them to take a time-out when they act up," said Rep. Spencer Bachus, R-Ala. "I think we are establishing a procedure similar to that with our markets when they do lapse into what happened last Thursday." 
 
 Both Schapiro and Gensler argued they have enough statutory authority to create circuit breakers across-the-board for exchanges. However, Gensler said legislation under consideration on Capitol Hill that would bring the over-the-counter derivatives market out of the dark onto transparent clearinghouses and exchanges would make it easier for the CFTC and SEC to determine the cause of future plunges. 
 
 "The reform [Congress] is moving in with the over-the-counter derivatives market will give us a greater understanding," Gensler said. "This review will enable us to have information about equities and futures market but not the over-the-counter derivatives market which may have played a role as well." 
 
 What didn't cause the plunge? 
 
 Schapiro refuted speculation that an exceptionally large order in shares of Procter & Gamble Co. /quotes/zigman/238894/delayed/quotes/nls/pg PG -0.34% , part of the Dow Jones Industrial Average /quotes/zigman/627449/realtime DJIA -0.28% , helped trigger the market decline. She also rebutted assertions on Wall Street that the drop may have been caused by hackers or terrorist activities. 
 
 "We have not identified any info consistent with computer hacker or terrorist activity," Schapiro said. 
 
 Lawmakers also squabbled over whether high frequency trading contributed to the market plunge. Rep. Brad Sherman, D-Calif., indicated he might support a minute tax on high frequency trades in the U.S. to limit their activities in the U.S. 
 
 "If most of the U.S. markets were insulated from high frequency trading, that's where most investors would want to go," Sherman said. ||||| The stock market plunged Thursday in a harrowing 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%, leaving Wall Street struggling to figure out what happened. 
 
 PM Report: Stocks Plunge, Fear Returns 9:41 The News Hub panel -- Neal Lipschutz and David Wessel in New York and Dave Kansas in London -- discuss today's market plunge. 
 
 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 Jones Industrial Average had crossed 10000 in the biggest intraday point drop in its history. By 3:07, the market had regained 500 points, ultimately staggering to a close at 10520.32, down 347.80 points. 
 
 The Securities and Exchange Commission and the Commodity Futures Trading Commission said they were working with other regulators to review "unusual trading activity." 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. 
 
 Dow Regains Some Ground View Slideshow Getty Images A man walks outside the New York Stock Exchange. 
 
 Multiple stocks, ranging from Accenture PLC to Boston Beer Co., momentarily lost nearly 100% 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 $9.5 billion iShares Russell 1000 Value Index Fund went from $59 to around 8 cents in the blink of an eye. 
 
 "It happened so quickly, it was like a torpedo," said Scott Redler, chief strategic officer at T3 Capital Management, a hedge fund. "It was mayhem." 
 
 Unnerved traders frantically searched for an explanation, scouring the trade blotters for clues to the cause. Many pinned the blame on an erroneous trade for a basket of stocks which caused shares for companies such as Procter & Gamble Co., one of the market's most stable blue-chip stocks, to fall 35% in two minutes. 
 
 The market was already down some 500 points when the selloff began. Televisions showed images of standoffs between Greek police and protesters, and the European Central Bank declined to step up its effort to stabilize government debt markets. 
 
 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. 
 
 Several high-frequency firms, including Tradebot Systems Inc., which says it often accounts for 5% of the U.S. market's volume, stopped trading when the market grew volatile. With these traders on the sidelines, there were fewer potential buyers, which may have contributed to the plunge. 
 
 —Jacob Bunge contributed to this article. 
 
 Write to Tom Lauricella at tom.lauricella@wsj.com ||||| * Shock slide in Dow triggers calls for crackdown 
 
 * High-frequency trading seen exacerbating plunge 
 
 * Slide might have begun with erroneous trade 
 
 * Senator urges "meaningful regulatory framework soon" 
 
 * Nasdaq, NYSE say they will cancel some trades (Adds Nasdaq and NYSE to cancel some trades, NYSE comment on advantage of human element, CME comment on Citigroup) 
 
 By Matthew Goldstein 
 
 NEW YORK, May 6 (Reuters) - A spine-chilling slide of nearly 1,000 points in the Dow Jones Industrial Average, its biggest intraday points drop ever, led to heightened calls for a crackdown on computer-driven high-frequency trading. 
 
 The slide, which in one 10-minute stretch knocked the index down nearly 700 points, may have been triggered by a trading error. Major stock indexes eventually recovered from their 9 percent drops to close down a little more than 3 percent. 
 
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 But the follow-through selling that pushed stocks of some highly regarded companies into tailspins exacerbated concerns that regulators can quickly lose control of the markets in a world of algorithmic trading. 
 
 High-speed trading, which uses sophisticated computer algorithms based on specific scenarios to automate transactions at speeds in the millionths of a second, now accounts for about 60 percent of U.S. equity volume. 
 
 "The potential for giant high-speed computers to generate false trades and create market chaos reared its head again today," Senator Edward Kaufman said in a statement.
– What's known in the business as a "fat finger" trade may have been responsible for yesterday's stock market chaos, analysts say. Multiple sources believe a trader at a major firm—possibly Citigroup—hit a "B" instead of an "M" while trading Procter & Gamble shares, selling a billion shares instead of a million, and sending the Dow Jones on a panicky rollercoaster ride. Major exchanges are also examining possible erroneous trades in multiple stocks that triggered glitches in the trading system, notes the Wall Street Journal. Traders were already nervous and the Greek crisis had been sending prices downward even before the panic, the New York Times notes. The plunge "happened so quickly, it was like a torpedo," said a chief strategic officer at a top hedge fund. "It was mayhem." The lesson from yesterday's chaos should be that "any market can fail temporarily," writes Felix Salmon at Reuters, predicting that the panic that hit markets yesterday will result in "increased volatility and risk aversion."