'Trolls' prompt UK debate over limits of internet free speech

If Twitter is the chirping chatterbox of the internet, trolls are its dark underground denizens.

The collision of the two is driving a debate in Britain about the scale of online hatred and the limits of internet free speech.

The furore erupted this week after several women went public about the sexually explicit and often luridly violent abuse they receive on Twitter from trolls - online bullies and provocateurs who send abusive messages.

Police are investigating a threat of rape and murder made to Labour Party lawmaker Stella Creasy. The graphically violent tweet was one of many Creasy received after supporting feminist campaigner Caroline Criado-Perez. Criado-Perez was sent a torrent of invective after she campaigned, successfully, for novelist Jane Austen to appear on a British banknote.

Two men have been arrested in connection with the Twitter threats, but have not been charged.

Police are also investigating threats against several female journalists after they received tweets warning them a bomb would detonate outside their homes at night.

Creasy and Criado-Perez are among a growing group who have decided to face down the abusers, re-tweeting their messages in an attempt to "name and shame" the offenders, and reporting the most threatening messages to police.

"This is not about Twitter," Creasy told the BBC. "This is about hatred of women and hatred of women who speak up."

Online trolls don't just target women, although women come in for a specific kind of abuse, says Claire Hardaker, a lecturer at Lancaster University in northwest England who researches aggression, deception and manipulation online.

Trolls pick out one defining characteristic to attack their victims, she said. "If you are a Muslim, it's all Islamophobia. If you are gay, it's all homophobia. If you are a woman, it's all misogyny."

British campaigners are calling for Twitter to do more to block bad behaviour. The site's rules explicitly bar threats of violence, but users currently have to fill out an online form to report abuse, a process some say is time-consuming and unwieldy.

Twitter insists it takes the issue seriously and is planning to expand an abuse-reporting button, already available on its iPhone app, to other platforms.

"We absolutely do work with law enforcement on issues like these," Del Harvey, Twitter's senior director of trust and safety, told the BBC's Newsnight programme. "These sorts of threats are against the rules. We suspend accounts when they're reported to us. We're working to make it easier to report those accounts."

Padraig Reidy of civil liberties group Index on Censorship cautioned that the "report abuse" button was no quick fix - it could itself be abused by governments to silence their opponents or by celebrities to muzzle their critics.