LinkedIn also said it has implemented new security measures to protect its users' personal information.
"We sincerely apologize for the inconvenience this has caused our members," Vicente Silveira, an engineering director for LinkedIn, wrote in a blog post. "We take the security of our members very seriously."
Silveira said the company is continuing to investigate how the breach occurred.
Sen. Patrick LeahyPatrick LeahyLive coverage: Day three of Supreme Court nominee hearing Dems land few punches on Gorsuch Live coverage: Day two of Supreme Court nominee hearing MORE (D-Vt.) and Rep. Mary Bono Mack (R-Calif.) expressed concern about LinkedIn's breach and said the incident shows the need for Congress to pass data security legislation.