It also recommended that users change their passwords at other sites where similar passwords are used.
Twitch is a multi-channel online network built for people who not only enjoy playing video games, but find it entertaining to watch others who might impart tricks and tips for excelling at their favorite games.
E-commerce giant Amazon.com Inc. bought Twitch for $970 million in 2014 as part of a move to take part in video gaming's growth as an online spectator sport.
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Twitch said it will communicate directly with affected users, according to the message sent Monday.
Figures from July 2014, just before the Amazon buyout, show that Twitch users viewed more than 15 billion minutes of content produced by more than 1 million broadcasters, ranging from individual gamers, pro players, video game publishers, developers and others.