Nasa has emailed its staff to warn them that hackers may have stolen their personal details.
The message said it suspected that two of its servers containing details of past and present employees had been compromised.
It added that it did not believe any Nasa mission had been put in jeopardy. One expert noted that this was the latest in a series of breaches experienced by the space agency to have been made public since 2011.
In this case, the memo involved was published by the SpaceRef news site.
It said that a probe into the incidents had been ongoing since 23 October.
“Our entire leadership team takes the protection of personal information very seriously,” it said.
“Nasa is continuing its efforts to secure all servers, and is reviewing its processes and procedures to ensure that the latest security practices are being followed throughout the agency.”
The email added that social security numbers and other private information belonging to civil service employees of the agency who had worked for it since July 2006, might have been affected.