The breach appears to have been aimed at unearthing the identities of Chinese intelligence operatives in the United States who may have been under surveillance by American law enforcement agencies.

It’s unclear how much the hackers were able to discover. But former U.S. officials familiar with the breach said the Chinese stood to gain valuable intelligence. The database included information about court orders authorizing surveillance — orders that could have signaled active espionage investigations into Chinese agents who maintained e-mail accounts through Google’s Gmail service.

“Knowing that you were subjects of an investigation allows them to take steps to destroy information, get people out of the country,” said one former official, who, like others interviewed for this article, spoke on the condition of anonymity to discuss a highly sensitive matter. The official said the Chinese could also have sought to deceive U.S. intelligence officials by conveying false or misleading information.

Although Google disclosed an intrusion by Chinese hackers in 2010, it made no reference to the breach of the database with information on court orders. That breach prompted deep concerns in Washington and led to a heated, months-long dispute between Google and the FBI and Justice Department over whether the FBI could access technical logs and other information about the breach, according to the officials…

“What we found was the attackers were actually looking for the accounts that we had lawful wiretap orders on,” David W. Aucsmith, senior director of Microsoft’s Institute for Advanced Technology in Governments, said at a conference near Washington, according to a recording of his remarks.