At any moment of the day or night, millions of children and teenagers are on line, exchanging e-mails and instant messages, surfing the World Wide Web and participating in chat rooms. Young people can get a lot of benefits from being online, but they might also be in danger.

A little beep coming from the computer in her family's living room alerted Jill Mentzer that an instant message had arrived for her 14-year-old daughter. Ms. Mentzer says she was shocked to see that it came from a 36-year-old man. "He asked if I would be willing to have sex with older men for money."

Ms. Mentzer told NBC News that she replied, pretending to be her daughter. "It just went on for 10 minutes. He wanted to know some private things about my daughter," she said. "I just kind of played it along with him. That's when we called the Sheriff and someone was there in 20 minutes."

The police wired Ms. Mentzer's daughter with a hidden microphone and watched as she went to meet this man in a fast food restaurant. They arrested him for attempted molestation and enticement of a minor. Ms. Mentzer said her daughter, who was well protected during the encounter, was happy to participate with police, because "she didn't want him doing it to anyone else."

While that particular predator has been caught, there are plenty of others like him still on-line.

According to children's advocate John Walsh, who founded the National Center for Missing and Exploited Children, Internet solicitation is one of the fast growing crimes today. "Cox Communication, the cable broadcasting company, did a national survey that says that 1 in 5 children are sexually solicited over the Internet," Mr. Walsh notes, adding, "only 1 in 4 ever report it."

Mr. Walsh says children are trusting, curious and eager to explore this new world, which is very accessible. They can go on line from personal computers at home, a friend's house, in school, a club or café. It's also possible to access the Internet on mobile devices such as cellular telephones. However, he says, parents still have a responsibility to protect their kids.

"Don't to assume it couldn't happen to you. I look back 24 years ago when my son was kidnapped and murdered. I didn't know what a pedophile was, I didn't think I would ever be a crime victim," Mr. Walsh says. He advises parents keep lines of communication open with their children. "I say to parents, 'Sit down with your kids, whether they are 10 or 18, sit down with them and say, "God, I love you so much. Let's learn the rules of protection.'"

Older parents may be at a disadvantage because they didn't grow up in the Internet Age. But John Walsh recommends that they develop their computer skills, and learn the lingo, or shorthand phrases kids use when chatting on-line.

"POS, for example, means parents over my shoulder, or P 9/11," he says. "Tell your kids don't give information. Don't give the address. Don't tell what you look like or what school you go to, or your phone number."

Mr. Walsh says monitoring kids' on-line adventures is critical to keeping them safe. But, according to Tina Schwartz of the National Center for Missing and Exploited Children, most parents don't know how to do that.

"We actually did focus groups with parents, and when we asked the parents if they monitored their kids' online activities, a lot of them said yes," she says. "When we asked what they did, a lot of them said they limited the hours their child is allowed online. That's not really monitoring what they are doing. It's not getting involved in communicating with our kids. So one of our main recommendations for parents is to talk to their kids and learn from their kids."

Ms. Schwartz says the Center for Missing and Exploited Children first addressed the issue of Internet safety 10 years ago.

"We created a brochure called 'Child Safety on the Information Highway.' That brochure is now been out for 10 years and we just keep adding to it," she says. "The risks change as the technology changes. Lots of information and resources [for parents and kids] can be accessed by going to our web site"

With June being designated Internet Safety Month by Congress, the National Center for Missing and Exploited Children has just launched a new public awareness campaign, targeting school kids as they begin summer vacation. Tina Schwartz says, with kids out of class and spending more time online, it's important to make sure they know the rules of the Web and the risks of unsafe surfing.