The New York Times said it had fallen victim to hackers possibly connected to China's military, linking the sophisticated attacks to its expose of the vast wealth amassed by Premier Wen Jiabao's family.
China, which has blocked the US newspaper's website ever since its report on Wen's relatives came out in October, said it was "groundless" to suggest any state-endorsed program of hacking.
"To arbitrarily assert and to conclude without hard evidence that China participated in such hacking attacks is totally irresponsible," Foreign Ministry spokesman Hong Lei told reporters in Beijing.
But computing experts hired by the New York Times to clean up its systems said the attack bore all the hallmarks of other hacking cases where China's military has stood accused of directing intrusions into IT systems.
The hackers have over the past four months infiltrated Times systems and snatched staff passwords, and their probing has been particularly focused on the emails of Shanghai bureau chief David Barboza, the newspaper said.
According to a Barboza story published on October 25, close relatives of Wen have made billions of dollars in business dealings over the years while he has been in day-to-day charge of China's government machinery.
"Chinese hackers, using methods that some consultants have associated with the Chinese military in the past, breached The Times's network," the newspaper said, citing digital evidence gathered by its security experts.
The newspaper said the IT consultants believed the attacks "started from the same university computers used by the Chinese military to attack United States military contractors in the past."
The hackers stole corporate passwords and targeted the computers of 53 employees including former Beijing bureau chief Jim Yardley, who is now the Times's South Asia bureau chief based in India.