Chinese hackers have repeatedly penetrated The New York Times' computer systems over the past four months, stealing reporters' passwords and hunting for files on an investigation into the wealth amassed by the family of a top Chinese leader, the newspaper has reported.
Security experts found that the attacks used tactics similar to previous hacking incidents traced to China.
The report said the hackers routed the attacks through computers at US universities, installed a strain of malicious software, or malware, associated with Chinese hackers and initiated the attacks from university computers previously used by the Chinese military to attack US military contractors.
The attacks, which began in mid-September, coincided with a Times investigation into how the relatives and family of Premier Wen Jiabao built a fortune worth over two billion US dollars (£1.3 billion).
The report embarrassed the Communist Party leadership, coming ahead of a fraught transition to new leaders and exposing deep-seated favouritism at a time when many Chinese are upset about a wealth gap.
Over the months of cyber-incursions, the hackers eventually lifted the computer passwords of all Times employees and used them to get into the personal computers of 53 employees.
None of the Times' customer data was compromised and information about the investigation into the Wen family remained protected, though it was unclear what data or communications the infiltrators accessed.
A Chinese Foreign Ministry spokesman called the Times' accusations groundless and reiterated the government's position that China also has been hacked repeatedly.
"To rashly jump to conclusions based on investigation results which have not been proved by evidence is totally irresponsible behaviour," the spokesman, Hong Lei, said at a routine daily media briefing. "China is also a victim of cyber-attacks. Chinese laws specifically stipulate that cyber-attacks are prohibited."
China has been accused by the US, other foreign governments and computer security experts of mounting a widespread, aggressive cyber-spying campaign for several years, trying to steal classified information and corporate secrets and to intimidate critics.