* Symantec says Hidden Lynx very likely based in China * Says it is not sure if group is linked to government * Says may be linked to well-known 2009 Operation Aurora By Jim Finkle BOSTON, Sept 17 (Reuters) - Researchers have discovered a group of highly sophisticated hackers operating for hire out of China, a U.S computer security company said on Tuesday, and it linked them to some of the best-known espionage attacks in recent years. Symantec Corp said the group, which it dubbed "Hidden Lynx," was among the most technically advanced of several dozen believed to be running cyber espionage operations out of China. Unlike a previous report by another company, Symantec did not accuse the Chinese government of involvement in the cyber attacks. Symantec's 28-page report described Hidden Lynx as a "professional organization" staffed by between 50 and 100 people with a variety of skills needed to breach networks and steal information, including valuable corporate secrets. The company said its researchers believed Hidden Lynx might have been involved with the 2009 Operation Aurora attacks, the most well-known cyber espionage campaign uncovered to date against U.S. companies. In Operation Aurora, hackers attacked Google Inc, Adobe Systems Inc and dozens of other companies. Google in January 2010 disclosed the attacks, in which hackers tried to read Gmail communications of human rights activists and to access and change source code at targeted companies. Dmitri Alperovitch, the researcher who named Operation Aurora in February 2010 when he was the first to uncover key details about the attacks, said he believed that Symantec's conclusions were generally accurate. Alperovitch, who is chief technology officer at the cyber security firm CrowdStrike, said his company has also linked Operation Aurora to other attacks by the same group including a high-profile breach at EMC Corp's RSA security company in 2011. CrowdStrike has not publicly shared details about the group, which it calls Aurora Panda, because the firm makes money by selling proprietary research to clients, he said. Symantec researcher Liam O'Murchu said his company could not determine which individuals were behind Hidden Lynx or if it was linked to the Chinese government. Alperovitch said, however, that CrowdStrike believes the group works solely for the Chinese government and state-owned enterprises. "Whether they are formally a military unit or a defense contractor, that is unknown," he added. A separate study released in February from Mandiant, another firm that closely follows Chinese hackers, said a secret unit of the Chinese military was engaged in cyber espionage on American companies. Beijing vehemently denied the accusations in that document, which contained photos of the building that Mandiant said was the unit's headquarters. () O'Murchu said Symantec believes Hidden Lynx is based in China because much of the infrastructure used to run the attacks is there and because the malicious software was written using Chinese tools and with Chinese code. The Symantec report attributed several recent attacks to Hidden Lynx, including a breach at cybersecurity firm Bit9 and follow-on attacks at three Bit9 clients. () It also connects Hidden Lynx to a major campaign dubbed Voho, which was discovered last year by EMC's Corp's RSA security company. Voho targeted hundreds of organizations, including financial service, technology and healthcare companies, defense contractors and government agencies. FINANCE TARGETED Symantec's report described the group as a "highly efficient team" capable of running multiple operations at once and of targeting specific organizations across a variety of industries. That profile suggests that they were hired by clients seeking out very specific pieces of data, the report said. For example, the financial services sector was the most heavily affected industry, representing about a quarter of targets since November 2011, according to Symantec. While Symantec would not identify particular victims within the financial industry, it said they included companies with information on pending merger and acquisition activity. Such information might prove valuable to Hidden Lynx clients in negotiating takeovers or trading shares. The victims did not include commercial banks, Symantec said. Hidden Lynx's arsenal of tools included Trojan Naid and Trojan Moudoor, which siphoned data from infected computers. Symantec, which sells software and services to protect corporate and consumer computer systems from cyber attacks like the ones mentioned in the report, said Naid was also used by hackers in Operation Aurora. The Hidden Lynx hackers "were either responsible for the Aurora attack or were working in conjunction with the Aurora attackers," O'Murchu said.