The episodes are hurtful, ugly -- and sometimes deadly. In Lakeland, Fla., a group of teenagers records the beating of another teen. The local sheriff says the attack was in retaliation for online trash-talking by the victim.

At a high school near Pittsburgh, an anonymous e-mail list features sexually explicit rankings of 25 female students, names and photos included.

In suburban Dardenne Prairie, Mo., near St. Louis, 13-year-old Megan Meier hangs herself after receiving cruel messages on the social-networking site MySpace.

In Essex Junction, Vt., 13-year-old Ryan Patrick Halligan kills himself after months of harassment, including instant messages calling him gay.

The cases, albeit extreme, highlight what school officials, child psychologists, legal experts and government researchers argue is a fast-spreading epidemic of "cyberbullying" -- the use of the Internet, cell phones and other digital technology to harass, intimidate, threaten, mock and defame.

Studies show cyberbullying affects millions of adolescents and young adults. The Centers for Disease Control and Prevention last year labeled "electronic aggression" -- its term for cyberbullying -- an emerging public-health problem.

A reliable profile of cyberbullying, a relatively new phenomenon, is difficult to construct. Studies leave little doubt, however, that cyberbullying is growing.

Some cyberbullies are angry loners, sometimes seeking revenge for having been bullied themselves. But experts say it is common for online abusers to be popular students who are trying to strengthen their place in the social hierarchy.

"It's not really the schoolyard thug character" in some cases, said Nancy Willard, executive director of the Center for Safe and Responsible Internet Use, a research and professional development organization in Eugene, Ore. "It's the in-crowd kids bullying those who don't rank high enough."

What fuels cyberbullying is "status in schools -- popularity, hierarchies, who's cool, who's not," said Danah Boyd, a fellow at the Berkman Center for Internet and Society at Harvard Law School who studies teens' behavior on MySpace, Facebook and other social-networking sites.

Of course, bullying itself is nothing new. What's new is the technology.

More than 90 percent of teens are online. More than half of online teens have profiles on social-networking sites.

The sites allow people to post personal facts, photos, gossip and other information for others to read. Social scientists say such sites can serve a useful, and even vital, purpose by helping adolescents build friendships, learn tolerance for others' views and form a sense of self-identity. But critics say the sites have the potential to be incubators for abuse, magnets for sexual predators and embarrassing archives of a student's immature behavior that college admissions officials or employers may wind up seeing.

The rise of Web sites brimming with the minutiae of teen antics and angst has helped to create a rich climate for mayhem: locker-room photos snapped with cell phones and broadcast on the Internet, fake profiles created on social-networking sites, salacious rumors spread in chat rooms, threats zapped across town in instant messages.

States step in

Cyberbullying has impelled lawmakers, especially at the state level, to either pass anti-bullying laws that encompass cyberbullying or add cyberbullying to existing statutes. Some laws are propelled by a mix of concern about electronic bullying and online sexual predators.

But using laws and courts to stop cyberbullying has been tricky and sometimes controversial. "There's a big conflict in knowing where to draw the line between things that are rude and things that are illegal," said Parry Aftab, an Internet privacy and security lawyer who is executive director of wiredsafety.org, an Internet safety group in Irvington-on-Hudson, N.Y.

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