The message board  changes its rules in May to prohibit attacks and harassment of individuals through the site. Harassment is defined as systematic or continued actions to torment or demean someone in a way that would make a reasonable person conclude that it is not a safe platform to express their ideas or participate in the conversation, or fear for their safety or of those around them.

The move follows the introduction of a revised privacy policy in February that prohibited Reddit users posting naked photos and sex videos if they lack permission from the people depicted.

Where to draw the line on free speech?
Where to draw the line on free speech?

On Wednesday, Reddit said it had banned the five subreddits, adding that the only one of those that had more than 5,000 subscribers was called "Fat People Hate." A link to this community said that the subreddit had been banned for violating Reddit rules.

The site wants as little involvement as possible in managing users' interactions, but will ban subreddits that are allowed by their communities to be used as a platform to harass individuals, if the moderators don't take action, interim chief executive Ellen Pao and two other site officials wrote in a blog post. "We're banning behaviour, not ideas," according to the post.

The latest change would not have an immediate noticeable effect on more than 99.99 percent of the site's users, Reddit said, but some Reddit users were, however, critical of the bans, with one predicting that it wouldn't go down well.

"I can't say I liked any of the 5 banned subs, but seems like freedom of expression shouldn't be banned," wrote another user. When the administrators' attention was pointed to other subreddits that were also offensive but not banned, the site claimed that the other reddits being referred to "might be hateful or distasteful, but were not actively engaging in organised harassment of individuals."

The changes at Reddit reflect growing concern about bullying, harassment and other crimes on the Internet, which has forced other social media companies to also change their policies. "