How a hacker stole 272.000.000 accounts?

A hacker from Russia seems to be…
it has managed to steal data from more than 272 million email accounts which sells them for 1 dollar each.
The web attack is considered by experts as one of the largest that have been made in the history of the internet and according to Hold Security, the majority of the accounts come from the Russian service Mail.ru and affects almost all users( 57 million. of the total 64 million. active users), while of course not miss the Yahoo (with 40 million. user accounts), Yahoo, Hotmail (with 33 million. accounts), and Gmail (to 24 million. accounts) .
The Russian hacker who seems to be responsible for the attack that he sells on the internet the details of the accounts for $1 each, while for the time being only the Mail.ru and Microsoft have acknowledged this threat while Yahoo and Google have not made any comment.
Those users believe they may have fallen victim to this attack, it is advisable to change the password and if they want (evil is not, in any case) to activate the function of two-step authentication in which the access becomes even more difficult to a third party after service of the request the 6-digit code that sends the mobile user.