Digital intruders have broken into News Corp email accounts and compromised the data of an unspecified number of journalists, the US company says.
The media firm's internet security adviser said the hack was likely aimed at gathering intelligence for Beijing's benefit.
News Corp, which publishes the Wall Street Journal, said the breach was discovered in late January and affected emails and documents of what it described as a limited number of employees, including journalists.
It said cybersecurity firm Mandiant had contained the breach.
David Wong, vice-president of consulting at Mandiant, said the hackers were believed to have "a China nexus, and we believe they are likely involved in espionage activities to collect intelligence to benefit China's interests".
A spokesman for the Chinese embassy in Washington said he was unaware of the details of the reports but that he hoped "there can be a professional, responsible and evidence-based approach to identifying cyber-related incidents, rather than making allegations based on speculations".
In a letter seen by Reuters, company executives told their employees that "we believe the activity affected a limited number of business email accounts and documents from News Corp headquarters, News Technology Services, Dow Jones, News UK, and New York Post".
"Our preliminary analysis indicates that foreign government involvement may be associated with this activity, and that some data was taken," executives said.
The company added that its other business units, including HarperCollins Publishers, Move, News Corp Australia, Foxtel, REA, and Storyful, were not targeted in the attack.
The Wall Street Journal, which reported the news first, competes with Reuters, the news division of Thomson Reuters Corp, in supplying news to media outlets.
Chinese hackers have repeatedly been blamed for hacks of journalists both in the United States and elsewhere.
In 2013, for example, the New York Times reported a breach which it said had affected 53 personal computers belonging to its employees.
The paper said the timing of those intrusions corresponded with its investigation into the wealth accumulated by relatives of Wen Jiabao, China's then-prime minister.
Australian Associated Press
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