You leave an electronic trail every time you use a credit card, rent a DVD, open a bank account or surf the Internet. That's a lot of personal information that could all too easily fall into the wrong hands. Last year 10 million Americans were victims of identity theft. In Prying Eyes, author Eric J. Gertler, former CEO of Privista, a software company that focuses on credit management and identity-theft protection, offers practical ways to maximize your privacy. Illustrated with real-life tales of ID theft, Gertler's book explains the preventive steps that could have been taken. Some of his ideas, such as not giving out your Social Security number unnecessarily, are not a surprise. But what is illuminating is the number of institutions and even government agencies from which you can withhold your number, as well as the opportunities you have to replace your Social Security number with a different ID digit on your driver's license, employee files and academic records.