Passwords were encrypted, but insecurely, and Leaked Source says it has managed to crack 99% of them.
It's not clear who was behind the attack, though Leaked Source says it occurred in October 2016.
"In no cases are we ever the only ones with leaked user data."Even users who once registered on one of Friend Finder's hookup or porn sites and later deleted their accounts may still be caught up in the data spill.
According to Leaked Source, 15 million of the breached usernames and passwords appear to have been from users who intended to delete their accounts but whose details were still retained by the company.
The 412 million accounts go back 20 years, it says, and the lion's share comes from Adult Friend Finder — almost 340 million.