“We’re cooperating with the FBI, which is actively investigating and asked us not to discuss who may be behind this attack.”

The FBI has asked Facebook not to reveal who may be behind a recent hack that exposed highly sensitive personal information of 14 million users, according to a Facebook security update Friday.

A hack on Facebook, which originally was reported to have affected 50 million users, now has been confirmed to have only affected 30 million. That said, the hack “appears to be the worst hack in Facebook’s 14-year history,” according to Business Insider’s Rob Price.

Hackers took advantage of an intersection of three different and distinct bugs in Facebook’s website to gain “access tokens” to users’ accounts, according to Guy Rosen, the vice president of product management at Facebook.