What do you have on your laptop that you might not want anyone else to see?Is there, for example, a record of your doctor visits and which medications you take? Some music downloaded from the Web that may or may not be copyright-compliant? How about the spreadsheet listing your employees, how much they make, and who may become part of your company's projected layoffs? Or the e-mail you sent to your senator complaining about the treatment you recently receiving from airport security personnel?

How would you like all that to be read by customs agents the next time you come back from, say, London?

A recent InformationWeek article described how former Anaheim, Calif., junior high school math teacher Michael Timothy Arnold's laptop, CDs, and memory stick were examined by border agents at the Los Angeles International Airport when he came back from the Philippines in 2005. A lower court found that the contents of electronic devices are even more personal than, say, a diary, and that agents must have reasonable suspicion before examining the contents. The government disagreed and is appealing. At least two organizations -- the Electronic Frontier Foundation and the Association of Corporate Travel Executives -- believe the ruling was correct and have filed an amicus brief with the court.

I usually go through my laptop before a business trip and check it for documents that should be deleted or encrypted -- for example, notes about an ongoing news story or some of the more sensitive interoffice memos that I receive. But besides securing my laptop against theft, should I also wonder whether it will be read by the security personnel at the airport? Should I need to examine the contents of my hard drive each time I fly to make sure that I'm not reading any suspicious texts, carrying around any suspicious videos, or writing any suspicious e-mails?

Some may say that if Mr. Arnold hadn't had illegal files in his computer -- according to the government, his computer contained images of child pornography -- he wouldn't have had anything to worry about. After all, it's only the guilty who have something to hide, right? Well ... no. History teaches us that the most innocuous evidence can be used by authorities to incriminate citizens.

Back in the 1950s, for example, people lost their jobs because they had, years before, belonged to (or given money to, or signed a petition from) organizations that, two decades later, were believed to have ties to (or to share goals with, or to be even vaguely sympathetic to) the Communist Party. Three centuries before that, people were imprisoned and burned as witches or wizards because they had the wrong types of herbs in their gardens or the wrong types of moles on their bodies, or had said the wrong thing to the wrong person at the wrong time.

We now confide many of the facts and events of our personal and professional lives to electronic information devices that we carry with us. It is important that we keep that information safe from random searches.