A 13-year-old California boy was molested at computer camp by a man he met through the Internet. In Georgia, a 40-year-old car dealer was charged with raping a girl, 13, he befriended in an online chat session. And in Connecticut, the body of 13-year-old girl was found in a ravine after a man she met online confessed that he strangled her.
Such cases - and studies showing that as many as one in seven children are sexually solicited online - fuel concerns that the Internet provides an anonymous venue for sexual predators to lure children.
Receiving particular scrutiny are social networks such as MySpace and Facebook, Web sites increasingly popular among teenagers that allow users to create detailed personal profiles and exchange messages, photos and videos.
Such sites offer little guarantee, however, that a member's online identity matches the member's real identity, raising fears that children might pretend to be adults or that pedophiles could prey on youngsters under the guise of being a peer.
This week, MySpace and the attorneys general of 49 states and the District of Columbia announced that they will try to develop technology to verify the ages and identities of new members, limiting the ability of users to masquerade online.
But experts say it is difficult, if not impossible, to absolutely verify a person's identity online. Developing such a system, they said, presents significant hurdles, particularly if it is intended to verify the age of children.
"I just don't think there's a technological way that we know of to verify someone is a particular age only online," said Avi E. Rubin, technical director of the Johns Hopkins Information Security Institute.
Several of the measures that MySpace and the attorneys general proposed to protect teenagers online are premised on verifying users' identities when they first sign up. For instance, MySpace plans to set profiles of 16- and 17-year-olds "private" by default and users over the age of 18 will be barred from browsing minors' profiles. Another proposal was to allow parents to submit their child's e-mail to a third-party registry to prevent it from being used to create a profile.
But putting restrictions on teenagers' profiles and limiting adult access to them doesn't guarantee that the teenager and adult didn't lie about their age in the first place, experts said. Nor does it prevent a child from creating a profile using an e-mail address that parents aren't aware of.
Scanning through social network profiles reveals that users are given wide latitude in how they portray themselves. Among the members of the Baltimore Orioles Fan Club on MySpace, for instance, is a Virginia man who posted a Hawaiian driver's license as his profile picture.
Closer inspection reveals the name on the license is McLovin, the monicker used in the 2007 film comedy Superbad by a teenage character trying to purchase alcohol with a fake I.D.
"It's actually not my license," explained the MySpace member, Marc Bethel, of Virginia Beach. "It's the fake ID from Superbad, but with my picture Photoshopped in there."
Though Bethel's intent was harmless, his homage to McLovin's comedic cinematic farce reflects a sobering truth about social networking sites: teenagers are known for their ingenuity in sidestepping rules.
"There's very little in the world more resourceful than a 16-year-old trying to get someplace they're not supposed to be - especially the things that are specifically designed for people over 18," said Hopkins' Rubin.
One hurdle is the lack of a centralized database of information on children that Web sites could use to identify a child's age. Most identity-verification online - required for shopping by online retailers - uses credit card numbers, which are then compared against a central database.
"The reality is people under 18 don't drive cars and they don't have credit cards," said Kerry Loftus, a spokeswoman for Verisign, a company that handles secure online transactions.
She added that biometric devices such as fingerprint scanners used to secure some computers and mobile phones have proved unreliable. "If you go on a plane and your hands swell, you can't get into your computer," she said.
Requiring a biometric device to access a social networking site would also limit users to certain computers. "You would be limiting mobility," she said. "If a person wants to log in to their account, but they aren't at a computer that has a fingerprint reader, they'd be out of luck."
One possibility, she said, is that social networking sites could use "one-time passwords," a technology being used by PayPal, Charles Schwab and Bank of America.
In such systems, in addition to their username and password, customers are mailed a plastic token that randomly generates a second password they must enter to access their accounts online.
One benefit, Loftus said, is that a person must provide an address to receive the token. She acknowledged, however, that people could still thwart safeguards by lying about their age.
Quinn Palmer, 16, of Towson said she has known friends under 14 to sign up for MySpace accounts even though the site bans children 13 and under. She said many of her friends have switched to Facebook accounts recently because Facebook profiles seem more secure.
She has never been approached by an adult stranger on either MySpace or Facebook, but she applauded the announcement that MySpace was looking for ways to prevent predators from soliciting children. "I think it's sort of disgusting that people do that," she said. "I think it's really sketchy."
Despite the technical difficulties, David Finkelhor, the director of the Crimes Against Children Research Center at the University of New Hampshire, commended MySpace and the attorneys general for their efforts.
In a 2006, Finkelhor found that one in seven children are sexually solicited online and that one in 33 are aggressively solicited. In a separate study he found that, over a one-year period, between 2001 and 2002, there had been 1,000 cases where someone was arrested for sex crimes against a juvenile where the Internet played a role in the crime.
"I really think the attorneys generals did a great thing to step into this vacuum and get this conversation going," Finkelhor said.
But he also cautioned that fears of online predation might be overblown and that the dynamics of such cases are misunderstood.
There is little evidence, he said, that the Internet or online social networks have led to more cases of sexual assaults on children, despite the solicitations.
He noted that since the early 1990s the incidence of sex crimes against children has dropped by about half, despite a steady growth in Internet use. "The Internet doesn't seem to be creating any kind of epidemic in sex crimes," he said. In fact, social networks might provide an outlet for adventurous or alienated youths to burn off steam or seek companionship, without taking real-world risks.
"If they want to take risks and flirt, 10 years ago they may have gone to some party they heard about or gone to some seedy bar, where in fact they might encounter a predator," he said. "On the Internet, at least that person can't reach out and pull them into an alley or a closet or something."
He said the best way to protect children is educating them about the dangers. Because the teenagers who fall victim to online predators are often alienated from their parents, he said, education programs should directly target children ages 13 to 15.
Sun reporter Liz Kay contributed to this article.