Authorities warn students about wide-open Web space.

Byline: Ben Schmitt, Chastity Pratt and Peggy Walsh-Sarnecki

DETROIT _ Talking to 1,400 high school and middle school kids about Internet safety Thursday, a retired cop asked how many of them pretend to be older when they log on to chat, make friends and post personal information on Web sites like MySpace.com.

More than half raised their hands.

"I was proving a point and told them: `Don't you think people on the other end are pretending to be younger?'" said Rob Nickel , a retired Ontario Provincial Police officer who spent seven years undercover. He communicated online with pedophiles before he would bust them.

But Nickel's message Thursday, as he lectured students in Guelph, Ontario, Canada, was not that kids should stay away from the Internet or that parents should unplug their children's computers. It was that they can't turn a blind eye to the risks of lying online or opening up to strangers who, despite their claims, could prove dangerous.

Southeastern Michigan got a jolting lesson about the potential dangers of so-called social-networking …