Social-networking sites can provide a safe place for kids to exchange messages and connect with friends. But if your child’s profile isn’t set up so that only trusted friends can see the content, it’s possible that everything he posts maybe seen by anyone who’s online. “About six months ago, I was contacted on Facebook by a guy in his 20s or SOs who had the same last name as me,” says Courtney Mannak, 18, a recent high school grad from Jupiter, FL. “He said that we were related, and he was able to determine which one of his uncles was my father and even tell me what my sister’s name was, all from information that was pieced together from my Facebook account. It turned out that he was legitimately related to me, but it was still scary having a stranger know so much about me.”

The two giants of social networking, MySpace and Facebook, have improved their privacy practices in recent years, giving users much better tools for controlling who sees what. Those age 18 and under who set up profiles, for instance, are now given fairly strict privacy settings as a default, assuming they’re honest about their ages. But many teens (not to mention their parents) don’t know how to fine-tune their settings to keep themselves as safe as possible.

Arnold Bell, assistant chief of the FBI’s Cyber Division Strategic Outreach and Initiatives Section, recommends sitting with your child when he sets up a Facebook or MySpace page and looking at the privacy settings, so you can make sure he chooses wisely. Experts advise using the strictest privacy settings (which are now generally automatic for kids 18 and under) from the start.

To do this on Facebook, go to the “Privacy Settings” link under “Settings” at the top right-hand corner of any page. Make sure all the menus under “Profile” and “Search” are set to “Only Friends”—meaning that only friends your child has approved can access his profile, photos, and other information—or possibly “Friends of Friends” if his goal is to connect with a broader group. On MySpace, find the privacy settings by clicking on the “MyAccount” link in the upper right-hand corner of any page. Then click “Privacy,” and look for a heading that says “Profile View- able By.” Click on “My Friends Only.”

You can also customize other options—such as not allowing photos of your child to be shared or e-mailed by others—on the same page.

If your child already has an online profile, check to see if it’s public by Googling his name or searching for him on Facebook or MySpace (you don’t need to be a member to do so). Better yet, says Vila, do it together: “Say, ‘I understand that these days anything that’s posted online is very tough to keep private. Why don’t we Google you to check if there’s anything that you don’t want out there?” Also Google a friend or two of his, to compare and contrast. “You can say, ‘This person has chosen to have this stuff about her online—what do you think about it?” says Vila. “It’s an opportunity for you to discuss what are the right values for your family.”

Word to the wise- Also step in if your child is using Twitter, the micro-blogging service where users post short updates, known as tweets. Many kids don’t realize these are completely public, akin to posting on a virtual global bulletin board. Help your child click on the “Protect My Updates” setting to control which members can follow what she posts. And if a stranger starts following her updates, she can restrict that person’s access by using the “Block” tool.