The data was posted on an online forum by hackers claiming to have access to the personal data of 120 million accounts, offering to sell them at 10 cents per profile, the BBC writes.
The BBC says it contacted 5 users (from Moscow, Belgorod and Perm) affected by the breach, who all confirmed that the texts available online were indeed their private Facebook messages.
The platform where the data was posted appears, or has been made to appear, to have Russian links, the BBC investigation found. It is attached to a St. Petersburg based IP address, the BBC said.