.hack is a series of single-player hack and slash developed for the PlayStation 2 console by CyberConnect2 and published by Bandai. The series of four games, titled .hack//Infection, .hack//Mutation, .hack//Outbreak, and .hack//Quarantine, features a " game within a game"; a fictional massively multiplayer online role-playing game (MMORPG) called The World which does not require the player to connect to the Internet. Players may transfer their characters and data between games in the series. Each game comes with an extra DVD containing an episode of .hack//Liminality, the accompanying original video animation series which details fictional events that occur concurrently with the games.
The games are part of a multimedia franchise called Project .hack which explores the mysterious origins of The World. Set after the events of the anime series .hack//Sign, the games focus on a player named Kite and his quest to discover why some users have become comatose as a result of playing The World. The search evolves into a deeper investigation of The World and its effects on the stability of the Internet.
Critics gave the series mixed reviews. It was praised for its unique setting and its commitment to preserve suspension of disbelief, as well as the character designs. However, it was criticized for uneven pacing and a lack of improvement between games. The commercial success of the franchise led to the production of .hack//frägment—a remake of the series with online capabilities—and .hack//G.U., another video game trilogy.
.hack (pronounced "dot-hack") is a Japanese multimedia franchise that encompasses two projects; Project .hack and .hack Conglomerate. Both projects were primarily created/developed by CyberConnect2, and published by Bandai. The series franchise revolves around an alternative history setting in the rise of the new millennium regarding the technological rise of a new version of the internet following a major global computer network disaster in the year 2005, and the mysterious events regarding the wildly popular in-universe MMORPG series The World. The series is mainly followed through anime and video game installations, and has been adapted through manga, novels and other related media.