Nassau Det. Peter Badalucco sees a darker side of what can happen on social networks.

Personal information such as birth dates, school names, cell phone numbers, hometowns — all can be used for identity theft or other scams. "What information you put out there is what's going to be taken," said Badalucco, who handles computer crimes.

He recalled a local case in which a man managed to guess a woman's Facebook password because of a name listed in her tagged photos.

Using the password, the man changed the woman's settings and uploaded nude photos of her that he found in her Yahoo! e-mail account — which used the same password.

Similarly, status updates announcing that a user is on vacation — or just at a dentist appointment — can be an invitation to those with bad intentions.

"You're telling everybody your house is free," Badalucco said. "It's fun and stuff like that, but people don't see what can possibly happen."

The fast-growing phenomenon of interacting online comes with its own set of pitfalls, from identity theft to cyberbullying. Social media sites are not only altering how people interact — they're also changing how police investigate Internet crimes and how school officials deal with rumors and bullying in cyberspace.

It's not the social network itself that leads to danger, said Parry Aftab, executive director of Wire Safety, a nonprofit New York Internet safety group that's on Facebook's safety advisory committee. Instead, danger lies in sharing information too widely — without making use of privacy settings to control who sees what. "Anything that can go wrong in the real world can go wrong in a cyber world," she said.

Especially at risk are inexperienced online users unfamiliar with the scope of the Internet. "When you have unsophisticated newbies, they may not know how to use their privacy settings," she said.

Still, even the younger crowd familiar with how to navigate Facebook can experience problems. Nassau Police Officer John Dockwell, who is assigned to brief students about Internet safety issues, said he's heard of a variety of dangerous situations on Facebook, from a football player posting a sex video of him and his girlfriend to accounts of hurtful gossip that spread quickly.