Facebook said on Friday that it was the subject of a "sophisticated attack" from hackers last month, but no user data was compromised.
Employees at the social network visited an infected site and its servers downloaded malicious software, or malware, from the mobile developer site.
"As soon as we discovered the presence of the malware, we remediated all infected machines, informed law enforcement, and began a significant investigation that continues to this day," the company said in a blog post Friday. "Facebook was not alone in this attack. It is clear that others were attacked and infiltrated recently as well."
Also read: Twitter Says 250,000 Accounts Hacked
The social network's engineers and outside security experts were continuing to investigate the hack on Friday to "learn everything we can about the attack, and how to prevent similar incidents in the future."
Earlier this month, Twitter said it was hacked, and it quickly reset the passwords of more than 250,000 profiles.