Facebook said on Tuesday that investigators have determined that hackers did not access other sites that use the social networking site's single sign-on in a massive cyber attack that the company disclosed last week.

"We analyzed third-party access during the time of the attack we have identified. That investigation has found no evidence that the attackers accessed any apps using Facebook Login," said Guy Rosen, a Facebook vice president overseeing security.

Facebook last week disclosed its worst-ever security breach, saying hackers had stolen login codes that allowed them to access nearly 50 million Facebook accounts.

Initially, it was believed that the hackers could have also accessed third-party websites and apps that allow uses to access their accounts using Facebook logins.