(NBC News) -- Facebook today announced that it was the target of a "sophisticated" hacking attempt in January, though the company assured its users that their data was not "compromised."
The information was communicated in a blog post by Facebook Security. The social network's security experts explained that a few employees had visited an infected site, which installed malware on their laptops via a then-unknown bug in Java. The laptops, Facebook noted in its defense, were "fully-patched and running up-to-date anti-virus software."
Suspicious activity was noted on Facebook's internal networks shortly thereafter, tracked to the laptops in question, and remedied; The Java exploit was reported to Oracle (which makes the Web app platform), which issued a patch on Feb. 1.
Facebook's Chief Security Officer, Joe Sullivan, told Ars Technica that the attackers "were trying to move laterally into our production environment," where they would have access to lots of private and proprietary data. They were stopped before that point, but could have collected some non-user data like corporate emails and some code.
"We have found no evidence that Facebook user data was compromised," the company wrote in the blog post. It also reported that it is working with law enforcement and other companies' security teams to analyze and prevent future breaches.