Then she was sent the address of a blog, or web diary, where she was stunned to find an entry claiming that she had a sexually transmitted disease. The final blow was an e-mailed photograph of her new boyfriend naked with another girl.

Another teenager warned online that she wanted to stab a boy’s eye out with a “really hot french fry”. One boy opened a web page inviting friends to comment on pictures of fat girls at his school. In one popular internet forum, dozens of teenagers posted mocking comments about a boy with serious acne.

Internet watchdogs are becoming increasingly concerned about the spread of so-called cyberbullying, an online abuse that has begun to hurt children across America — mostly without their parents realising that anything is amiss.

“We are all familiar with school bullies,” said Parry Aftab, a lawyer who specialises in internet privacy. “Cyberbullying is the online equivalent. It is any kind of harassment, insult or humiliation that uses internet-related technology.”

Aftab will join a large group of teachers, parents and internet safety experts at a New York conference on cyberbullying this week. It is one of the first significant attempts to alert parents to a largely invisible form of teenage intimidation spawned by the worldwide vogue for camera phones, text messaging and internet chat rooms.

Researchers who have studied teenage internet use have discovered websites where children vote for the ugliest, most unpopular or fattest girl in their school. “As teenagers increasingly turn to blogs, some of these diaries have become a hotbed of cruelties,” Aftab added.

On one popular website, a 17-year-old boy invited his friends to “take a moment and really think about who you hate in our school, then choose the one that you have the most disdain for and write it here for all to see”. His message drew 240 replies and featured everyone from “that stupid blind girl” to a school dinner lady.

At a Boston school recently, several students were disciplined for creating a lewd website about a teenage girl’s supposed sexual activities. The site included her name, photograph and phone number. In New York a 14-year-old girl who foolishly sent her boyfriend a camera phone picture of herself topless was mortified when he posted it on a website used by everyone at their school.

“We’re only seeing the tip of the iceberg,” said Edward Lee, principal of a Boston school. Lee said he first became aware of the problem when an outbreak of fighting in class was traced to online insults.

Experts are warning parents that their children may be reluctant to admit to being the victims of cyberbullying.

“A kid who gets beaten up in school has to go home with a black eye or a split lip or a chipped tooth,” said Jon Lieberman, a clinical psychologist. “A kid that gets beaten up on the internet doesn’t show those physical indicators. But some kids are tortured unmercifully.”

Aftab claimed there were several instances of children committing suicide after being ridiculed or humiliated online.

The problem is said to be particularly acute in prosperous suburbs, where teenagers tend to have “lots of technology, too much time on their hands and not enough parental supervision”, Aftab said.

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