For the past four months, Chinese hackers have persistently attacked The New York Times , infiltrating its computer systems and getting passwords for its reporters and other employees.

After surreptitiously tracking the intruders to study their movements and help erect better defences to block them, The Times and computer security experts have expelled the attackers and kept them from breaking back in.

The timing of the attacks coincided with the reporting for a Times investigation, published online October 25, that found that the relatives of Wen Jiabao, China’s Prime Minister, had accumulated a fortune worth several billion dollars through business dealings.

Security experts hired by The Times to detect and block the computer attacks gathered digital evidence that Chinese hackers, using methods that some consultants have associated with the Chinese military in the past, breached The Times’ network. They broke into the email accounts of its Shanghai bureau chief, David Barboza, who wrote the reports on Mr. Wen’s relatives, and Jim Yardley, The Times’ South Asia bureau chief in India, who previously worked as bureau chief in Beijing.

“Computer security experts found no evidence that sensitive emails or files from the reporting of our articles about the Wen family were accessed, downloaded or copied,” said Jill Abramson, Executive Editor of The Times .

The hackers tried to cloak the source of the attacks on The Times by first penetrating computers at U.S. universities and routing the attacks through them, said computer security experts at Mandiant, the company hired by The Times . This matches the subterfuge used in many other attacks that Mandiant has tracked to China.

The attackers first installed malware malicious software that enabled them to gain entry to any computer on The Times’ network. The malware was identified by computer security experts as a specific strain associated with computer attacks originating in China. More evidence of the source, experts said, was that the attacks started from the same university computers used by the Chinese military to attack U.S. military contractors in the past. — New York Times News Service