As many as one in three U.S. children have been ridiculed or threatened through computer messages, according to one estimate of the emerging problem of cyberbullying.
Another new study found the problem is less common, with one in 10 kids reporting online harassment.
But health experts said even the lower estimate signals a growing and concerning public health issue.
"I wouldn't consider something that 10 percent of kids report as low," said Janis Wolak, a University of New Hampshire researcher who co-authored the second study.
Wolak and other researchers, though, found that in many cases the incidents of online harassment were relatively mild.
The U.S. Centers for Disease Control and Prevention is trying to draw attention to how U.S. adolescents are affected by e-mail, instant messaging, text messaging, blog postings and other electronic communications.
Last year, CDC officials convened a panel of experts to focus on the topic. They also funded a special issue of the Journal of Adolescent Health to publish more research on the subject. The journal released the articles Tuesday.
It's difficult to say how severe online harassment is as a public health issue, because a posting or e-mail that might upset some children is shrugged off by others, CDC officials said.
And the result of surveys can differ depending on how questions are asked.
But the issue was attracted the attention of lawmakers in Oregon, Washington, New Jersey and other states that have introduced bills or instituted programs designed to reduce cyberbullying. Last week, officials in a Missouri town made Internet harassment a misdemeanor, after public outrage over the suicide of a 13-year-old resident last year.
The parents of Megan Meier claim their daughter, who had been treated for depression, committed suicide after a teenage boy who flirted with her on MySpace abruptly ended their friendship, telling her he heard she was cruel. The story gained national prominence this month when it was revealed the boy never existed _ it was a prank allegedly started by a mother in the girl's neighborhood.
The schoolyard continues to be a source of in-person bullying: Studies indicate roughly 17 percent of early adolescents say they are victims of recurring verbal aggression or physical harassment.
Some kids suffer both in-person and electronic harassment, but it's more often one or the other. A study by California-based researcher Michele Ybarra found 64 percent of youths who were harassed online were not also bullied in person.
The new studies made conflicting estimates of the size of the problem. The largest estimate came from Ybarra, president of Internet Solutions for Kids, a nonprofit research organization.
One Ybarra study was based on an online survey of 1,588 children ages 10 to 15. It found 34 percent said they were the victim of Internet harassment at least once in the previous year, and 8 percent said they were targeted monthly or more often.
Also, 15 percent said they're received at least one unwanted sexual communication in the past year. That included solicitations for sex or conversations about sex or questions about bra size or other personal sexual information.
All bothersome communications were included, no matter the age of the sender.
Wolak's study was a telephone survey of 1,500 Internet users, ages 10 to 17. The 9 percent who said they were harassed online in the previous year was an increase from the 6 percent in a similar study in 2000.
At least part of the difference may lie in how the surveys were done: The New Hampshire study defined online harassment as anyone who said they felt embarrassed, worried or threatened by an online posting or Internet message. Ybarra's survey asked not only whether someone made aggressive or threatening comments, but also whether someone had made rude or mean comments or spread rumors about them.
In the Wolak study, more than half of the communications came from people that the children had never met. Many were easily handled by deleting the comment or blocking additional postings from the sender.
"A lot of the kids were not particularly upset," Wolak said.
Because much of the online aggression is not a recurring harassment, she and others said "cyberbullying" probably isn't the best description.
"Most of these are pretty brief encounters," she said.