Facebook has announced that it was the target of a "sophisticated attack" by hackers last month, but said it found no evidence of user data being compromised.
The social network said that the attack occurred when employees visited a mobile developer website "that was compromised" and led to malware being installed on their laptops.
The US-based company said that it has fixed the infected machines, informed the authorities and initiated an investigation.
It reassures users that there is no evidence of their data being at risk and that it continues to work with law enforcement to prevent future attacks.
Many companies affected
In a post on its security blog, Facebook said that it was not the only company to have been attacked in this way.
"As one of the first companies to discover this malware, we immediately took steps to start sharing details about the infiltration with the other companies and entities that were affected," the social network said in a statement.
"We plan to continue collaborating on this incident through an informal working group and other means."
Under Facebook's White Hat programme, anyone who finds a way of breaching the site's networks and owns up can earn rewards worth thousands of dollars.
In addition to reward money, the site promises not to press criminal charges providing they comply with the programme's golden rules.
"If you give us reasonable time to respond to your report before making any information public, and make a good faith effort to avoid privacy violations, destruction of data and interruption or degradation of our service during your research, we will not bring any lawsuit against you or ask law enforcement to investigate you," Facebook said in a statement announcing the programme last year.