Hackers attack Facebook's internal network

The attackers were able to access the tech giant's computer network after employees visited a mobile developer's website which downloaded malware - software often used to steal information - onto employees' laptops.

"As soon as we discovered the presence of the malware, we remediated all infected machines, informed law enforcement, and began a significant investigation that continues to this day," the company wrote in a blog post.

The staffers whose laptops were infected were found to be running up-to-date anti-virus software. But the attackers used what is known as a "zero-day" exploit, software that exploits previously unknown flaws in computer software, making it almost impossible for anti-virus software to detect.

The flaw was found in a piece of Java software, and Facebook said it has reported the vulnerability to Oracle, the company that makes the software.

Java has been the centre of a global security scare.

Last month the US Department of Homeland Security urged people to disable Java software after hackers figured out how to install software that enabled them to steal users' identity, credit card and banking information and attack other websites.

Facebook said it was not alone in the attack and said "others were attacked and infiltrated recently as well", though it did not name the affected companies.

"We plan to continue collaborating on this incident through an informal working group and other means," the company said.

The social network is adamant that no user data was compromised.

Java was contacted for comment.