The accusations came after the 14-year-old posted online several photos of a dog. The photos were taken two years ago. The dog belonged to one of her classmates and she was keeping it temporarily at her home.

In a message, the girl said she once accidentally hit the dog and it died two weeks later.

The teenager said the photos were meant to pay tribute to the dog. But her posting led some of her internet friends to believe she was responsible for the animal's death.

Within three days, a discussion group was set up on Facebook to condemn the girl. More than 11,000 netizens joined the forum and wrote hundreds of nasty comments.

Other angry internet users created profiles of the girl and put them online. They contained a lot of personal details, such as her name, photos, MSN account, e-mail address, the name of her school and some of her daily routines.

The girl who owned the dog defended her classmate, claiming that it had been suffering from parasite problems and the blow had nothing to do with its death. But her clarification did not stop the vicious messages.

The incident caused the girl so much distress that she could not go to school.

According to Chinese media reports, the student had to stay home for days and received counselling from social workers.

Internet users call the attempt to identify and expose an individual's private details a 'background dig-out' or a 'human flesh search'. It involves massive collaboration to piece together all the details of a person's life and then publish them online.

The girl's case is the latest in a string of cyber bullying in recent years. In November, a City University student became the victim of a cyber attack.

An internet user, claiming to be a teenage girl, posted a message on a discussion forum, accusing the student of pushing her off the stairs after making her pregnant.

Facebook users set up groups to criticise the young man. His personal details, including his home address and telephone number, were uploaded online. He reported the matter to the police after receiving hundreds of nasty telephone calls.

Human flesh searches, aimed as retaliation for so-called social injustice or reckless behaviour, are usually triggered by media reports, photographs, videos or even a brief comment posted on blogs or discussion groups.

However, it becomes a problem when the information is not true.

Ng Kam-kuen, a senior social worker with the Hong Kong Federation of Youth Groups, said cyber bullies acted out of hatred of their target.

'In these cases, many young people join the bullying under peer pressure. Most of them also don't bother to find out the truth,' she said. 'They only follow what their friends are doing. And most of these attacks are personal rather than topical.'

Attackers take advantage of the power of the internet to spread the message to millions of cyber users, and the victims can do little about it.

'The insulting messages spread on the internet really fast. Even if you delete a message this minute, another can emerge the next,' said Howard Song Zhaoxun, associate professor at Shue Yan University's journalism and communication department.

He said cyber bullying could kill. Many attackers are unaware of the psychological damage they are causing their victims, he added.