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 A group of Russian hackers infiltrated the servers of Dow Jones & Co., owner of the Wall Street Journal and several other news publications, and stole information to trade on before it became public, according to four people familiar with the matter. 
 
 The Federal Bureau of Investigation, Secret Service and the Securities and Exchange Commission are leading an investigation of the infiltration, according to the people. The probe began at least a year ago, one of them said. 
 
 Dow Jones, in a statement, said: “Since Bloomberg published its article, we have worked hard to establish whether the allegations it contains are correct. To date, we have been unable to find evidence of any such investigation.” 
 
 The breach is described by the people familiar with it as far more serious than a lower-grade intrusion disclosed a week ago by Dow Jones, a unit of Rupert Murdoch’s News Corp. The company said last week that it is working with a cybersecurity firm and law enforcement after learning that hackers had sought contact and payment information of about 3,500 customers. 
 
 It’s unclear whether the incursions are related. It’s also unclear whether the company’s news-gathering operations were affected in the insider-trading matter. Two of the people familiar with the investigation said the hackers sought information including stories being prepared for publication. 
 
 Kelly Langmesser, a spokeswoman for the FBI New York office, confirmed the office is investigating a breach at Dow Jones but declined to comment further. Jim Margolin, a spokesman for the Manhattan U.S. Attorney’s Office, declined to comment. Peter Carr, a spokesman for the Justice Department’s criminal division, also declined to comment, as did spokesmen for the Secret Service and the SEC. 
 
 The White House was briefed on the investigation and the FBI and SEC have spent months trying to determine exactly how the hackers could profit from what they took, consulting financial and market experts among other specialists, the people said. 
 
 Information embargoed by companies and the government for release at a later time could be valuable to traders looking to gain an edge over other market participants, as could stories being prepared on topics like mergers and acquisitions that move stock prices. 
 
 Dow Jones publishes the Wall Street Journal and Barron’s and provides information through a number of services including Dow Jones Newswires. Bloomberg LP, the parent of Bloomberg News, competes with News Corp. in providing financial news and services. 
 
 New Front 
 
 The hack investigation shows how quickly law enforcers are shifting to a new front in insider trading: cyberspace. Market-moving, nonpublic information used to trade hands in secret meetings. Hackers are now stealing sensitive information and selling it to traders. This new vulnerability in the financial markets is challenging law-enforcement officials who are trying to keep pace with cyber-criminals’ rapidly evolving moneymaking schemes. 
 
 For would-be inside traders, business journalists and data providers are a rich target. Potentially market-moving scoops often develop in-house for days or weeks, promising intruders a long pre-publication window to mine information and execute trades. Data being held for public release at a specified time can also be a gold mine in markets where the profitably of a trade is determined in a fraction of a second. 
 
 Dow Jones says in its annual report that its Factiva service provides global business content to about 1.1 million active users. “More than 4,000 sources make information available via Factiva on or before the date of publication by the source,” according to the report. Dow Jones Newswires publishes more than 16,000 news items each day to financial professionals and investors. 
 
 Hacking for Tips 
 
 U.S. authorities are ramping up their pursuit of hackers after a series of high-profile attacks on corporations. 
 
 In August, federal authorities made several arrests in what they called a years-long scheme that fused insider trading and hacking. In that matter, Russian-speaking hackers working from Ukraine were indicted along with traders for siphoning more than 150,000 press releases, including corporate earnings containing data that could be used to anticipate stock market moves, prosecutors said. 
 
 Those hackers broke into the servers of PRNewswire Association LLC, Marketwired and Business Wire, a unit of Warren Buffett’s Berkshire Hathaway Inc., over a five-year period, according to prosecutors. The group allegedly made more than $100 million in trades using unreleased earnings releases of companies such as Panera Bread Co., Boeing Co., Caterpillar Inc. and Oracle Corp., through retail brokerage accounts. 
 
 For more, read this next: 
 
 QuickTake: Cybersecurity 
 
 Information companies are regularly bombarded by hackers. When he disclosed the customer-data breach on Oct. 9, Dow Jones Chief Executive Officer William Lewis said the incursion was part of a “broader campaign involving a number of other victim companies.” Dow Jones learned of the hack from law enforcement officials, Lewis wrote, saying it had determined its system was breached at times between August 2012 and July 2015 by hackers whose goal appeared to be gathering contact information for customers so it could send them fraudulent solicitations. The company said it had no direct evidence that information was stolen. 
 
 — With assistance by Gerry Smith, and Chris Strohm 
 
 (Updates with further Dow Jones statement in third paragraph.) ||||| Dow Jones servers were infiltrated by a group of Russian hackers looking for stock tips, Bloomberg reported Friday. 
 
 The Federal Bureau of Investigation's New York office confirmed to CNBC that it is aware of the hack and is investigating. 
 
 In a statement, Dow Jones said, "to the best of our knowledge, we have received no information from the authorities about any such alleged matter." 
 
 "We are looking into whether there is any truth whatsoever to this report by a competitor news organization," Dow Jones said. ||||| Alcoa Inc., Hewlett-Packard Co. and Bank of America Corp. will be dropped from the Dow Jones Industrial Average next week, in the biggest shake-up of the 30-stock index in almost a decade. 
 
 Alcoa, a Dow component for 54 years, will be replaced by athletic-gear maker Nike Inc. Payments company Visa Inc. will replace H-P, which joined the index in 1997, and securities firm Goldman Sachs Group Inc. will supplant Bank of America, which spent five years in the blue-chip benchmark. 
 
 The Dow undergoes major overhaul as it drops Alcoa, Hewlett-Packard, and Bank of America, and adds Goldman Sachs, Nike and Visa. This change marks the biggest DJIA change in decades. David Blitzer, managing director and chairman of the Index Committee S&P; Dow Jones Indices, joins MoneyBeat. 
 
 The Dow's Ins and Outs Changes since the late 1980s. View Graphics 
 
 For the new entrants, "it would be very hard to argue that these are three companies not worthy of inclusion," said Dan Greenhaus, chief global strategist at New York brokerage BTIG LLC. "It's a positive development in the sense that you're trying to make the index better with each passing day." 
 
 "When you go out to the bar at night, or you go home and you say 'What did the stock market do today?' the majority of people will go, 'Oh, the Dow was up 50 points, or the Dow jumped 300 points,'" Mr. Greenhaus said. "It's the number that most people, when they think of the stock market, refer to." 
 
 The changes, which will take effect with the close of trading on Sept. 20, "were prompted by the low stock price of the three companies slated for removal and the Index Committee's desire to diversify the sector and industry group representation of the index," S&P Dow Jones Indices LLC, the company that oversees the Dow, said in a statement. 
 
 Chris Dieterich joins the News Hub with a look at today's market action, including breaking news about the biggest change to the Dow 30 composition in a decade. 
 
 S&P Dow Jones Indices is a unit of McGraw Hill Financial Inc. CME Group Inc. and Dow Jones & Co., a unit of News Corp that publishes The Wall Street Journal, own stakes in S&P Dow Jones Indices. 
 
 While their performance has been mixed this year—H-P is up more than 50%, while Alcoa is down about 7%—all three departing stocks have underperformed the broader stock market in recent years. Shares of New York aluminum maker Alcoa closed Monday at $8.06, down from $40 as recently as 2007. H-P, the Palo Alto, Calif., computer maker, ended at $22.27, down from $50 in 2010. Bank of America of Charlotte, N.C., finished at $14.61, down from $50 in 2007. 
 
 Goldman Sachs shares rose 3.5%, while Visa gained 3.4% and Nike added 2.2%. Alcoa's shares slipped 0.3%, while H-P dropped 0.4%. Bank of America rose 0.9%. 
 
 "We are pleased to join this historic and significant market benchmark, and remain dedicated to delivering value for our shareholders as a member of the Dow 30," a Goldman Sachs spokesman said. 
 
 In a statement, Alcoa said: "The composition of the Dow Jones Industrial Average has no impact on Alcoa's ability to successfully execute our strategy, and we remain focused on delivering shareholder value. 
 
 "This decision has no impact on our business or our strategy for providing solid returns to shareholders," Bank of America said in a statement. 
 
 A Visa spokesman didn't have an immediate comment. Representatives for H-P and Nike couldn't be reached for comment. 
 
 S&P Dow Jones said the moves won't have any effect on the level of the index, which finished Tuesday at 15191.06. 
 
 The Dow is a price-weighted measure, meaning the bigger the stock price, the larger the sway for a particular component, and vice versa. That is different from indexes such as the Standard & Poor's 500, which are weighted by components' market capitalizations. 
 
 David Blitzer, chairman of the index committee at S&P Dow Jones Indices, said the methodology for calculating the Dow allows for the companies to exit and enter without affecting the measure's level. The value following the moves will be "100% dependent on what the market does and not on these changes," Mr. Blitzer said on a conference call. 
 
 While a big change for the Dow industrials, observers say the impact on the individual stocks should be limited. That is because unlike other well-known indexes, such as the S&P 500 or the Russell 2000, relatively few index-tracking investment products follow the Dow and will need to buy or sell shares based on the changes. 
 
 "Despite the popularity of the Dow Jones Industrial Average in the press, it's a lot less significant than an add to the Russell 2000 or an add to the S&P 500, because it's just not an index that institutions benchmark to," said Phil Mackintosh, global head of trading strategy at Credit Suisse Group AG. 
 
 The Dow move is the biggest since April 2004, when American International Group Inc., Pfizer Inc. and Verizon Communications Inc. replaced AT&T Inc., Eastman Kodak Co. and International Paper Co. Numerous changes have taken place since. A year ago, insurer UnitedHealth Group Inc. replaced Kraft Foods Inc., as the global snacks company moved toward a spinoff of its North American grocery business. The committee that determines the blue-chip average's makeup said Kraft's reduced size made it unfit. 
 
 In June 2009, Citigroup Inc. was replaced by insurer Travelers Cos., and General Motors Corp. was supplanted by networking company Cisco Systems Inc. 
 
 Citigroup was recovering with U.S. government assistance from a brush with death during the financial crisis, and General Motors had just filed for bankruptcy. A successor company, General Motors Co., emerged from bankruptcy the next month. 
 
 In September 2008, Kraft Foods joined the Dow, replacing AIG following the government's decision to take a 79.9% stake in the insurance heavyweight. That February, Bank of America and Chevron Corp. had replaced Altria Group Inc., formerly known as Philip Morris Cos., and Honeywell International Inc. 
 
 —Andrew R. Johnson contributed to this article. 
 
 Corrections & Amplifications 
 
 The Dow Jones Industrial Average closed Tuesday at 15191.06, leaving it up 16% for the year to date. An earlier version of this article gave an incorrect closing figure and year-to-date performance data. 
 
 Write to Matt Jarzemsky at matthew.jarzemsky@dowjones.com 
 
 A version of this article appeared September 11, 2013, on page C1 in the U.S. edition of The Wall Street Journal, with the headline: Reshuffle of DJIA Adds Nike,Visa and Goldman.
– Citing interviews with four anonymous sources, Bloomberg reports Russian hackers broke into Dow Jones & Co. servers a year or so ago and stole stock information before it was public. Dow Jones, which is part of News Corp and owns the Wall Street Journal, claims it's unaware of any such hack, despite the FBI confirming the incident to both Bloomberg and CNBC. "We are looking into whether there is any truth whatsoever to this report by a competitor news organization," Dow Jones says in a statement released to CNBC. The FBI and Securities and Exchange Commission have spent months trying to figure out how hackers could profit from what they stole, concluding they were likely looking for stock tips contained in embargoed information and unpublished stories, Bloomberg reports. Dow Jones admitted to another cybersecurity breach last week in which hackers tried to get contact and payment information from around 3,500 customers. According to Bloomberg's sources, this new hack is more serious than the one Dow Jones addressed publicly. It's unclear if the two incidents are related.