Faceook says the FBI has asked it not to reveal who might be behind a hack that affected 30 million users.

On Friday, Facebook provided more details about a major hack of its systems that it first dislcosed two weeks ago.

"We’re cooperating with the FBI, which is actively investigating and asked us not to discuss who may be behind this attack," Facebook exec Guy Rosen wrote in a blog post.

"We now know that fewer people were impacted than we originally thought. Of the 50 million people whose access tokens we believed were affected, about 30 million actually had their tokens stolen."

This story is developing...