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Closing down the places internet trolls gather can help to stop the spread of hateful comments on social media, suggests research.

US scientists studied what happened on Reddit after it took action in 2015 to close down offensive chat forums.

The ban led many people to close their Reddit accounts and those that stayed toned down their language, they found.

However, the study suggests that the ban did not have a significant impact beyond Reddit.

For their study the researchers from Georgia Tech, Emory University in Atlanta and the University of Michigan analysed data on more than 100 million comments and posts put on Reddit before and after the ban.

"The ban worked for Reddit," said the study. "It succeeded on both a user and community level."

The social news site took the step of banning forums, known as subreddits, because they were acting as rallying points for trolls who targeted, for instance, black people or those who were overweight.

At the time the ban was enacted in 2015, Reddit boss Steve Huffman said the site was created to support "open and honest discussion" rather than as a "bastion of free speech".

The research looked at what happened in response to the ban by analysing the activity of people who joined in discussions on the banned forums.

On the two main banned subreddits, 41% and 33% of users respectively stopped posting or deleted their accounts.

The remainder that stayed also moderated their speech by as much as 80%, suggests linguistic analysis by the researchers.

Trolling was kept at a low level by ensuring duplicate offensive forums were quickly shut down, it said.

The ban meant the amount of hate speech flowing into and across Reddit declined by a "large and significant" amount, said the study.

The overall effect on attitudes and activity across the net was more muted, said the researchers. This was because many people who left Reddit as a result of the ban just jumped to another social network that did not moderate what they said.

Reddit's ban effectively made the actions of the trolls "someone else's problem" said the social scientists, and "likely did not make the internet safer or less hateful".

Social media expert Whitney Philips told technology website Motherboard that while it was good that Reddit had taken a stance, it was important to grasp the true extent of the problem.

"Studies like this that are limited to a specific platform can create a sense of false security because it's not looking at the whole landscape," she said.