Be careful what you post. Students are getting expelled for what they post on social Web sites. With recent news coverage of the sites and their explosive growth, <A HREF="http://www.usatoday.com/tech/news/internetprivacy/2006-03-08-facebook-myspace_x.htm?csp=34">authorities have taken notice,</A> concerned not only about inappropriate behavior but that kids are making themselves vulnerable to predators. Police recently have investigated several cases involving teens who were sexually assaulted by men they met on these sites. Earlier this week, two men were indicted on federal charges that they used the Internet to have sexual contact with girls from Connecticut.