Miss New Jersey thought her online photos were private. So did an "American Idol" contestant from Point Pleasant. Amy Polumbo and Antonella Barba instead discovered that their racy just-for-fun photos, posted on members-only sites such as Facebook and MySpace, were accessible to everyone, including would-be blackmailers with modems. But it's not just Jersey girls who fail to realize that deleting images and gossip from Web pages -- or placing them in password-restricted areas -- can't keep them from prying eyes. Many people are at risk because they don't understand how data are stored and shared. "When you delete it, content...