Dell SecureWorks said the attacks have been traced to servers in two Chinese major cities - Beijing and Shanghai.
A nation state was behind the attacks, dubbed "Operation Shady RAT," said Dmitri Alperovitch, McAfee Vice President of Threat Research. But Alperovitch declined to go into detail.
"The most likely candidate is China," said James A. Lewis, a cybersecurity expert at the Center for Strategic and International Studies. "This isn't the first we've seen. This has been going on from China since at least 1998."
China's government has yet not given any official comments. But the country has consistently denied all charges of hacking in the past.
China's state media was reportedly told by McAfee experts that they "don't have direct evidence that conclusively points to a particular nation state" such as China is behind the "Operation Shady RAT."
China's Communist Party newspaper, the People's Daily, said "linking China with Internet hackers is irresponsible."
"[S]ome Western media have repeatedly described China as 'the black hand behind the scenes.'"
According to McAfee's report on Wednesday, the attacks have stolen closely guarded national secrets (including from classified government networks), source code, bug databases, email archives, negotiation plans and exploration details for new oil and gas field auctions, document stores, legal contracts, SCADA configurations, design schematics and much more.
"This is the biggest transfer of wealth in terms of intellectual property in history," Alperovitch said. "The scale at which this is occurring is really, really frightening."
"Companies and government agencies are getting raped and pillaged every day," he added. "They are losing economic advantage and national secrets to unscrupulous competitors."
In addition, even though most of the evidence suggests China might be the perpetrator, the United Nations, the U.S. and other international organizations are facing other potential cyber-enemies, such as Iran and Terrorists.