Apparently MangaTrader has been hacked and everyone's username/password has been gotten a hold of and a lot of them have been posted online in a list for everyone to see.
If you were a member on there and your log in credentials are the same password as what you use to log in to your e-mail, you might want to change your password if you care about your e-mail account possibly being taken over.
Im not saying it will happen but I am saying it can happen if the password used on the site is the same as you use to get into your e-mail account.
Once someone gets in that e-mail account, they can pretty much take control of whatever else you registered that e-mail account under if they desire.
If you don't care about the account or the e-mail because it was only for MangaTrader and thats it, then I guess there's no worries on your part.