Well, it doesn't matter. If you do any of the things I listed, it will be why you lose your account.
Doesn't matter that it was months ago, or that it was on a different computer. It's also possible that it just took that long for this to happen.
Or, you can just not be giving us all the information. Only you know the truth, but I assure you, that it is highly unlikely to lose ones account unless the attacker actually KNOWS who to attack.