ATLANTA — Facebook says the FBI is investigating a major security breach of its service, but the company says authorities asked it not to discuss who may be behind the attack.
That suggests Facebook may know or suspect who's behind the breach.
When Facebook disclosed the breach two weeks ago, company officials said they didn't know who was behind the attacks or where they might be based.
Facebook is disclosing for the first time that hackers accessed data from 29 million accounts as part of the breach. The exact number hadn't been known before.
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For 14 million of those accounts, hackers got even more data, such as hometown, birth date, the last 10 places they checked into or 15 most recent searches.
One million accounts were affected but hackers didn't gain information.
The social media service plans to send messages to people whose accounts were hacked.
Originally Facebook said 50 million accounts could have been affected, but Facebook didn't know if they had been misused.
Facebook says third-party apps and Facebook apps like WhatsApp and Instagram are unaffected.
The Associated Press contributed to this report.