From UK Anime Network News:
Security breaches of web sites big and small is a sad but unavoidable part of the online landscape at this point in time, and we’ve just received word from visual novel distributor MangaGamer that they have suffered from just such a breach in the past few hours.
The e-mail notification of an intrusion upon their database reports that no credit card information has been compromised, but that user names, passwords and e-mail addresses have potentially been accessed. As always in such a scenario, the advice is to change the password on any accounts you might have at MangaGamer, while any identical passwords used on other services should also be changed to protect yourself.
Read more on UK Anime Network News. They do not mention whether the passwords were hashed or not.
h/t, @VERISDB