Facebook says it was the target of a "sophisticated attack" after a handful of employees visited a compromised mobile developer website last month.
Malware was installed on the laptops of some Facebook employees.
The laptops were immediately patched and authorities were notified. Facebook says it has no evidence suggesting Facebook user data was compromised.
The social networking company says a significant investigation is under way.
"Facebook, like every significant internet service, is frequently targeted by those who want to disrupt or access our data and infrastructure. As such, we invest heavily in preventing, detecting, and responding to threats that target our infrastructure, and we never stop working to protect the people who use our service," said the company.
Facebook says it wasn't alone in the attack, and says it was one of the first to find out about the malware. The company then notified other organizations.
Facebook is encouraging users to let them know about any security issues by submitting the problem in its Bug Bounty Program.
For more information visit Facebook's security section here: https://www.facebook.com/notes/facebook-security/protecting-people-on-facebook/10151249208250766