I am SO glad that mine are grown now and that I don't have to worry about all this! The scary thing is, you can take all the precautions, be as vigilant as is humanly possible, monitor them every minute they are on the computer, and they can still do like my friends' daughter did - go to a friends house and post it from there!
Raising kids is a whole lot more difficult now than it was just a few years ago. I don't envy any of you!