Deep Blue was a chess computer constructed at IBM. After losing a match to then-world champion Garry Kasparov in 1996, a new version of the machine (informally dubbed "Deeper Blue") defeated Kasparov 2-1-3 in a six-game match in 1997. The final and decisive game of the latter series was decided after an opening blunder by Kasparov as white against the Alekhine defense was answered by a sharp rook sacrifice from the computer. Following this defeat, Kasparov cried foul and complained that the computer had been modified in the middle of the match, demanding a rematch. None was granted, however, and the machine was disassembled. The construction of the computer is detailed in the book Behind Deep Blue: Building the Computer that Defeated the World Chess Champion, by Feng-hsiung Hsu, who played an important role in Deep Blue's creation.