Almost two-thirds of parents admit to monitoring which Web sites their teenagers visit, according to a survey released by the Pew Internet & American Life Project.

But Parry Aftab, an online privacy expert and advocate for child safety, says parental snooping into teens' Web surfing should be reserved for situations in which they may be at risk, not a common practice. It's better to talk to teens about their Web habits, make them aware of the online risks such as sexual predators and cyberbullying, and limit the time they spend online, she says.

"Don't snoop, not unless you've got a child who's at high risk. Then you don't have a choice," says Aftab, who is founder and executive director of WiredKids.org, a Web site that promotes online safety for kids, and TeenAngels.org, an affiliated site for teen volunteers who educate their peers about safe surfing. High-risk teens include drug users or those known to meet with strangers they originally met online. Aftab also is a columnist who writes about privacy issues on InformationWeek.com.

Aftab recommends parents install Web-monitoring software such as SpectorSoft Corp.'s Spector application, which records E-mail, instant messaging, screenshots, and key strokes, in addition to Web sites visited. But she says parents should only review the information collected as a last resort. If a teen is missing and foul play suspected, the monitoring software can reveal whom he or she may have been communicating with online. "It's like the security video camera in the corner of the coffee shop," Aftab says.

Given the potential dangers, teens need to learn how to use good judgment when using the Web and other electronic media, including online games and cell phones. Aftab says the "filter between their ears" is more important than Web-filtering software on a PC.

"The newest issue is cyberbullying," Aftab says. "It ranges from 'I hate you' [ messages] to taking your head and putting it on a pornographic image." Aftab's organization has created a Web site, StopCyberBullying.org, to educate kids and parents about the threat.

When a parent recently told Aftab that his daughter had established "many" screen names for instant messaging, Aftab said it was a warning sign the girl was being harassed. She advised the parent to confront the daughter about potential problems and insist that she reduce those online IDs.

Practicing online safety is equally important for preteens, Aftab says. "We have to focus on the middle schoolers," she says. "It's crucial that kids understand what they should and shouldn't do in connection with the new technology tools."