Risky behavior on social networking sites

In the second study, Moreno sent an e-mail message to half of 190 young people from 18 to 20 years old whose public MySpace profiles included at least three references to sexual behaviors or substance use, including alcohol and tobacco. She called herself "Dr. Meg," identified herself as an adolescent medicine doctor and researcher, and urged them to check out her academic Web page.

"You seemed to be quite open about sexual issues or other behaviors such as drinking or smoking," the message said. "Are you sure that's a good idea? After all, if I could see it, nearly anybody could."

The message invited them to consider revising their profiles to protect their privacy. It also raised concerns about sexually transmitted diseases and pointed them to a Web site offering free testing.

Three months later, 42.1 percent of the ones who received the e-mail had changed their profiles, dropping references to sex and substance use or moving their profiles from public to private. That compares to 29.5 percent from the other half of the study group, who changed their profiles without having gotten Dr. Meg's e-mail.

Dr. Michael Rich, director of the Center on Media and Child Health at Children's Hospital Boston, was impressed that one well-phrased e-mail message could have such a strong effect on the adolescents in the study.

"They believed that e-mail whether they should have or not," he said, doubting that the young people verified who "Dr. Meg" was. "It brought them up a little bit short to see 'someone out there is actually paying attention to what I am doing.' "

Rich, who was not involved in either study, sees social networking sites as venues where young people channel their images and ideas, connecting with peers as they try on different identities -- the way their parents might have done on the telephone. Where they can get into trouble is believing what they put on their profiles remains anonymous, outside their circle of friends, he said.

"The Internet is not only the village square, but what they put there never leaves," he said. "They have to be prepared to take responsibility for the images and ideas they present."

Using such sites to promote health messages is promising, Kimberly J. Mitchell and Michele Ybarra of the University of New Hampshire's Crimes Against Children Research Center said in an editorial appearing with the two studies.

"Youth will likely be more receptive to prevention and intervention messages if they can relate to them on a personal level using the technology they inhabit," they write. "At the same time, we need to be aware that adolescents see their profiles as their private space."

Rather than pushing advice into their domains, pulling them into nonjudgmental information sites might have a better chance of success, Rich of Children's said. An online resource could "friend" a person who has a profile, for example.

There's a risk that young people will leave these Web 2.0 social networking sites behind for the next big thing.

"E-mail is so old," Rich said. "Instant messaging and texting are fading away for Twitter, which is much more immediate. It just shows how quickly technology transforms the world we live in and the way we do things."