Facebook said it was the target of hackers but no user information was compromised during the attack.

The social media giant said on Friday on its security blog that the company discovered in January that its system had been targeted in a sophisticated attack. The attack occurred when a handful of the company’s employees visited a developer’s compromised website, which led to malware being installed on their laptops.

Facebook said it has found no evidence that user data was compromised.

The company has fixed the infected machines, and an investigation is under way. Facebook also said it was not the only company targeted in the attacks but was one of the first to discover it.