no offense but this is a BS
guys who do this never use accounts they got, well they use accs like rs premium, but they just dont have time to mess with some game called magicduel, if you understand what i mean, they get tons of user/pass all the time, they dont have time to use them, they sell them or share them, give away, they dont keep them, they make them public somewhere as a proof of work they have done and to show that they are capable of work so they get respect and reputation in community in which they are
only if someone actually had her as target may be using her account, but usually for stuff like this you dont have target, only if it is becoz of some personal issues, and then it isnt worth of risk, thats why i think it was done by some random guy, and someone else is now using her account
and kafuuka already said many methods, and still it isnt event half of possibilities
edit: oh so after all it was a personal thing, sry i misread it, things like that are very rare