Hackers attack Facebook's internal network

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Facebook revealed on Saturday that its internal network was hacked last month.

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.