WASHINGTON — Chinese government hackers who breached Google’s servers in recent years gained access to a sensitive database with years’ worth of information about American surveillance targets, according to current and former US government officials.
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 US 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 sensitive matter.
The official said the Chinese could also have sought to deceive US 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.
Google declined to comment for this article, as did the FBI.
Last month, a senior Microsoft official suggested that Chinese hackers had targeted the company’s servers about the same time Google’s system was compromised. The official said Microsoft concluded that whoever was behind the breach was seeking to identify accounts that had been tagged for surveillance by US national security and law enforcement agencies.
‘‘What we found was the attackers were actually looking for the accounts that we had lawful wiretap orders on,’’ David 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.
‘‘If you want to find out if your agents, if you will, have been discovered, you can try to break into the FBI to find out that way. Presumably that’s difficult. Or you can break into the people that the courts have served paper on and see if you can find it that way. That’s essentially what we think they were trolling for, at least in our case,’’ he said.
Microsoft now disputes that its servers had been compromised as part of the cyberespionage campaign that targeted Google and about 20 other companies. Aucsmith, who cited that campaign in his remarks, said in a statement to the Washington Post that his comments were ‘‘not meant to cite any specific Microsoft analysis or findings about motive or attacks.’’
The US government has been concerned about Chinese hacking since at least the early 2000s, when network intrusions were discovered at US energy labs and defense contractors. The FBI has for years led a national security investigation into Chinese cyberespionage, some of which has been linked to the Chinese military.
The Chinese, according to government, academic, and industry analysts, have stolen massive volumes of data from companies in sectors including defense, technology, aerospace, and oil and gas.
The Chinese emphatically deny that they are engaged in hacking into US computer systems and have said that many intrusions into their own networks emanate from servers in the United States.
‘‘The Chinese government prohibits online criminal offenses of all forms, including cyberattack and cyberespionage, and has done what it can to combat such activities in accordance with Chinese laws,’’ a Chinese Embassy spokesman, Yuan Gao, said in an e-mail.
Google’s crisis began in December 2009, when, several former government officials said, the firm discovered that Chinese hackers had penetrated its corporate networks through ‘‘spear phishing’’ — a technique in which an employee was effectively deceived into clicking a bogus link that downloads a malicious program. The hackers had been rooting around inside Google’s servers for at least a year.
Alarmed by the scope and audacity of the breach, the company went public with the news in January 2010.
As Google was responding to the breach, its technicians made another startling discovery: its database with years’ worth of information on surveillance orders had been hacked. The database included data on thousands of orders issued by judges around the country to law enforcement agents seeking to monitor suspects’ e-mails.
The most sensitive orders, however, came from a federal court that approves surveillance on foreign targets such as spies, diplomats, suspected terrorists and agents of other governments.