In an official blog post, Twitch said that there had been "unauthorized access to some" user account information. The platform, where people can go to watch others play video games, draws in over 100 million unique users per month.
"For your protection, we have expired passwords and stream keys and have disconnected accounts from Twitter and YouTube," the company said.
"As a result, you will be prompted to create a new password the next time you attempt to log into your Twitch account."
Twitch also said that users should change their passwords on other sites where they have used the same or similar password. The company declined to give any further information about the attack when contacted by CNBC.
Twitch is the biggest platform for viewing e-sports - competitive video gaming where teams compete against each other in popular titles such as "League of Legends".
The e-sports industry is experiencing rapid growth, with global e-sports revenues set to hit $465 million in 2017 from $194 million last year, according to games market research firm Newzoo.
In August, Amazon purchased Twitch for $970 million in an effort to cash in on the growing e-sports hype.