Great article about hacking passwords on Ars Technica: http://arstechnica.com/security/2013/03/how-i-became-a-password-cracker/
But what I don't understand is why? From a black hat's standpoint, what's the benefit of having a list of passwords if you don't have the usernames/emails associated with them? Or are the usernames usually associated with password leaks?
I'm just confused because there's all this talk about passwords, but no talk about usernames. What's so beneficial to a hacker about a list passwords? To try on another attack when you have a specific username?