She'll talk about her unnerving findings Saturday at Miami Book Fair International. Among the alarming revelations (and there are many): Data aggregators not only sell your information to advertisers but also make it available to other parties, where it can be used against you by a prospective employer, a credit card company, a stalker -- or in a court of law.

 

"I think people realize if they put a drunken photo on Facebook it might hurt their chances with employers, but people may not realize searches on private emails can be used to make judgments," Andrews says. "If over Gmail I say to my sister, 'I'm thinking about getting a divorce,' I could be offered less-good credit cards because people going through a divorce are less likely to pay their credit card bills.