The Twitch accounts of PlayStation, Xbox and ESL were compromised overnight.
Polygon reports that a number of videos were renamed to include racist and homophobic language. Others were changed to messages making fun of Microsoft's Rise of the Tomb Raider exclusivity while some were altered to appear as if they were announcing new games such as Fallout 4.
Lots of archived videos were also deleted.
Twitch believes that the alterations were made at Gamescom on machines that were left legitimately logged in to the relevant Twitch accounts.
"We're deleting the offensive VODs as soon as we find them and are alerting individual teams at the venue," Twitch said. "As a precautionary measure, we temporarily removed highlights and past broadcasts for those channels since it's in the early hours of the morning in Cologne."