Facebook, which claims more than one billion users worldwide, says it was the target of a sophisticated computer attack last month.
The website said Friday that no customer information was compromised and that federal authorities are investigating.
It gave few details on the hacking but said it was discovered by tracing a suspicious file to laptop computers belonging to employees.
Facebook says it was not alone and that several other companies were also attacked.
Twitter reported a cyber attack earlier this month. The New York Times and Wall Street Journal newspapers have also said they were attacked and blame computer hackers based in China.
U.S. President Barack Obama issued an executive order this week for more protection from cyber attacks on critical infrastructure.