Nicola Brookes wasn't even a big Facebook user - "I only had nine 'friends' at the time" - when she posted a supportive comment about Frankie Cocozza, the X Factor contestant, after he'd been kicked off the show. So she was completely unprepared for the torrent of abuse that followed.
Her simple message ("Keep your chin up, Frankie. They'll move on to someone else soon") sparked months of cyberabuse in which Brookes, a 45-year-old single mother from Brighton, found herself falsely accused of being a drug dealer, prostitute and child abuser. Her home address was published online. A fake profile was set up in her name, from which explicit messages were sent to thousands of other internet users, including young girls.
"It was vile and depraved. But I don't feel the police did anything to help," said Brookes this week. "They just told me to close my Facebook account and my friends to do the same. But I don't think that's right… stealing someone's identity, stealing a photo to hurt and harass them."
Last week, Brookes won a landmark legal case, in which the High Court ordered that Facebook disclose the identities of the "trolls", the anonymous internet bullies who had made her life such a misery. But her seven-month fight with the internet giant has taken its toll. The single mother, who suffers from Crohn's Disease, has found her condition flare up again from the stress. "I've had my daughter in tears, begging me, 'Drop this [campaign] - it's going to kill you.' But I can't give up. I feel some relief now that this is finally being taken seriously."
Brookes is not the only one to find that Facebook - and, indeed, the entire online world - can be a savage place. Take the 60-year-old who was conned out of thousands of pounds; the grieving parents forced to confront doctored pictures of their dead son; and the 12-year-old groomed and then raped by an older man. These are very different crimes, but with one big similarity: they are the latest manifestations of how crime is migrating online, and how behaviour that would never be tolerated in real life can often be found in the virtual world.
Earlier this week, Sue Berelowitz, Deputy Children's Commissioner for England, told a home affairs select committee how the internet was enabling the sexual exploitation of children, and that lone paedophiles using computers could now commit abuse as easily in "leafy rural areas" as in inner cities. "Parents may think they can control what's going on because they can have a block on the computer. But the reality is children can get anything they like on their mobile phones. And they do."
Her evidence to MPs came days after a newspaper survey claimed that a crime linked to Facebook is now reported every 40 minutes. Last year, officers logged 12,300 alleged offences with links to the social networking site. The offences ranged from the apparently trivial - someone harassing a parent with messages about why their child hadn't been invited to a birthday party - to the serious: a bus driver grooming a 14-year-old boy, having become "friends" on the site, then sending him sexually explicit messages.
Experts are increasingly concerned that we are not getting to grips with crime committed online, a concern intensified by reports that Facebook is considering plans to allow under-13s on the website for the first time.
Police forces are having to dedicate increasing amounts of time to tackling cybercrime - a Freedom of Information request earlier this year revealed that Avon and Somerset Police has seen the number of crimes logged in which Facebook is mentioned jump from 190 in 2009 to 578 two years later. However, Facebook completely rejects the "one crime every 40 minutes" headlines, pointing out that the figure refers only to mentions of the website in crime logs.
"Just like mobile phones and TVs, Facebook is part of our everyday lives," said a spokesman. "When matters of serious criminality are found on Facebook, we work with law enforcement to bring those responsible to justice."
Yet three quarters of people who contact the National Stalking Helpline are targeted via emails and the internet, with social networking sites now featuring in one in six cases. "If someone in your workplace put up a picture of you or sent you abusive messages or letters, you would have recourse in law," says Richard Piggin, deputy CEO of the charity Beatbullying. "But we have to ask: are these laws fit for purpose in an online context?"
Children are particularly vulnerable to cyberbullying; a survey of 2,500 children carried out by the charity found that 50 per cent had been bullied in this way. Piggin is clear that it can have devastating consequences. "We're talking about loss of self-esteem, self-confidence and it can lead to self-harm or even suicide. These social networking groups are often disguised - set up with names like 'Emma's Fan Club' - but inside they can have very explicit, nasty stuff, death threats. We've seen comments like: 'I wish you were dead. It's [sic] better if you weren't there.' "
Robert Mullaney is still haunted by the day in 2010 that he found the body of his 15-year-old son, Tom, in the family garden. The teenager, an ardent Birmingham City fan, had hanged himself, the Mullaneys believe, after he had suffered bullying on Facebook. Worse still, even after he was dead, internet trolls desecrated an online tribute site, posting doctored photos of Tom with a noose around his neck and the caption: "Hang in there, Tom!"
The Mullaneys' case was not an isolated one. After Natasha MacBryde threw herself under a train in February 2011 after being bullied on the social networking site Formspring, her devastated family had to put up with vile messages, including a spoof picture called "Tasha MacTank engine" in which Natasha's photograph was superimposed on the front of the children's character. In one of the first cases of its kind, a 25-year-old internet troll called Sean Duffy was later jailed for 18 weeks for the abuse he had posted on Natasha's and other tribute sites.
There are also concerns from children's charities that social networking sites are used by predators to groom children. The case that hit the headlines was that of Ashleigh Hall, the 17-year-old trainee nurse who was murdered in 2009 by serial rapist Peter Chapman after he had posed as a teenager on the site. But last year Humberside Police revealed that Nicholas Bull, who was jailed for nine years for raping a 12-year-old girl he had met on Facebook, had contacted at least 40 girls online - and probably many more. The force also arrested a Hull mathematics teacher who had bombarded a pupil with 150 messages via the site, and who was eventually jailed for 15 years after he was found guilty of rape.
This week, a social networking game called Habbo Hotel, which has children as young as nine among its 250 million registered players, was revealed to contain pornographic sexual chat between users. Since December, at least two British paedophiles have been jailed after using the site to make contact with their young victims.
"The work we've done makes it clear that adults are targeting young people," says Jon Brown of the NSPCC. "We hear of children being made to perform abusive sexual acts online and then being filmed, or being groomed and encouraged to meet up with adults where they fall prey to sexual abuse. We have to take really seriously the fact that children are accessing Facebook from an early age - either because the age verification is rudimentary or because parents open Facebook accounts for their children."
Under current terms and conditions, no one under 13 is permitted to hold a Facebook account, and those aged 13 to 18 are given special protection that limits what details they can post, including their current location. But a survey of 4,000 children carried out by Professor Andy Phippen, of Plymouth University, found that nearly 40 per cent of primary school pupils are already on Facebook. While Brown feels strongly that under-13s shouldn't be on the site at all, Phippen takes a more pragmatic view, arguing that since so many children use social networking, the key is more education and training.
"If children did not have to lie about their age, and security was made tighter, that would be a good thing," says Phippen. "Parents have to play their parts. They have to be responsible in looking after their children."
A spokesman for Facebook said: "We are constantly innovating to protect minors online. We also believe that safety is a shared responsibility, involving companies like ours, parents, educators, law enforcement and policy-makers."
Meanwhile, Nicola Brookes is relieved that the social networking site will soon divulge the identity of her trolls for potential prosecution. But she is also aware that her case has not solved the problem. "If anything, the abuse has intensified and spread to other social networking sites," she said. "It's reached ridiculous proportions. There have been times when I've despaired. But you've got to keep on."
Additional reporting by Jo Heinemeier