Facebook’s internal computer network has been breached in a ‘sophisticated attack’ by hackers, but the company says no users were affected.

On Friday, the social media company announced that hackers targeted its computer system in January when Facebook employees visited an infected website that belonged to an unnamed mobile developer. As a result, malicious software was downloaded onto their laptops.

“As soon as we discovered the presence of the malware, we remediated all infected machines, informed law enforcements, and began a significant investigation that continues to this day,” Facebook said in a statement.

According to the company, others were also attacked by the hackers, who used a “zero day” exploit, a brand new type of malware that security tools cannot detect.

Engineers at Facebook and external security experts are reportedly working to “learn everything we can about the attack, and how to prevent similar incidents in the future.”

Facebook informed Oracle that the hackers used its Java software to infect the laptops.

Over the past year, Oracle has faced a wave of criticism over its Java programming language.

The Russian security company Kaspersky Lab says Java software was responsible for almost half of all the cyber attacks in 2012.

In response to the situation, many security experts have advised computer users to disable Java from their Web browsers to prevent attacks.