.hack (pronounced "dot-hack") is a series of single-player action role-playing games for the PlayStation 2, developed by CyberConnect2 and published by Bandai. The four games are titled .hack//Infection, .hack//Mutation, .hack//Outbreak, and .hack//Quarantine. The series features a "game within a game", a fictional massively multiplayer online role-playing game (MMORPG) called The World, without requiring the player to connect to the Internet. When players complete a game, they may transfer their characters and save data from one game in the series to the next. Each game also comes with an extra DVD containing an episode from the accompanying original video animation series .hack//Liminality, which details fictional events that occur concurrently with the games.