Washington â€"  A federal appeals court has turned down a Freedom of Information Act request to disclose National Security Agency records about the 2010 cyberattack on Google users in China.

The Electronic Privacy Information Center, which focuses on privacy and civil liberties, sought communications between Google and the NSA, which conducts worldwide electronic surveillance and protects the U.S. government from such spying. But the NSA refused to confirm or deny whether it had any relationship with Google. The NSA argued that doing so could make U.S. government information systems vulnerable to attack.

A federal district court judge sided with the NSA last year, and on Friday, a three-judge panel of the U.S. Court of Appeals for the District of Columbia upheld the ruling.

In 2010, Google complained about major attacks on its website by Chinese hackers and suggested the Chinese government may have instigated them. The Chinese government denied any involvement. Soon after, there were news reports that Google was teaming up with the NSA to analyze the attack and help prevent future ones.

The privacy center's FOIA request drew a "Glomar" response, in which an agency refuses to confirm or deny the existence of records. The term refers to a case in the 1970s, when the CIA refused to confirm or deny the existence of the Glomar Explorer, a ship disguised as an ocean mining vessel that the CIA used to salvage a sunken Soviet submarine. Courts consistently have upheld Glomar responses.

"In reviewing an agency's Glomar response, this court exercises caution when the information requested" involves national security, Judge Janice Rogers Brown wrote in the unanimous appeals court panel's ruling. "NSA need not make a specific showing of potential harm to national security in order to justify withholding information" under one of the law's exemptions because Congress has already, in enacting the FOIA statute, decided that disclosure of NSA activities is potentially harmful.

Brown said the question was whether acknowledging the existence or nonexistence of the requested material would reveal an NSA activity. The privacy center argued that some of the records it sought -- unsolicited communications from Google to NSA -- are not covered by exemptions cited by the NSA.

"The existence of a relationship or communications between the NSA and any private company certainly constitutes an `activity' of the agency" subject to exemption, Brown wrote. "Whether the relationship -- or any communications pertaining to the relationship -- were initiated by Google or NSA is irrelevant to our analysis."

"Moreover," she added, "if private entities knew that any of their attempts to reach out to NSA could be made public through a FOIA request, they might hesitate or decline to contact the agency, thereby hindering its information assurance mission," which focuses on protecting national security information and information systems.

Brown, an appointee of former President George W. Bush, was joined in the ruling by Judges Brett Kavanaugh, another George W. Bush appointee, and Douglas Ginsburg, who was appointed by former President Ronald Reagan.