Hackers manage to plant malicious code on the website's computers, but the company insists its user data was not compromised.
Facebook has revealed it was the victim of a sophisticated attack by an unknown hacking group last month.
The site's security was breached after a handful of Facebook employees unknowingly visited a website that had been compromised with malicious code.
When a suspicious file was discovered on the company's computers, a forensic investigation was launched and the origin of the file was traced to an employee's laptop.
A further search uncovered other infected computers, but Facebook insists there was no data breach and no passwords or user data were compromised.
more here:
http://news.sky.com/story/1052865/facebook-targeted-in-zero-day-hack-attack