If I should lose my drive, I don't care if someone sees what's inside. I do care, however, if somebody managed to tamper with any one of my files without my permission. If there's a program that will run on Windows and Mac that I can load onto my USB drive, that would be fine. You know what? I could create one, using my Java skills - after all, it's a pretty safe bet that every device into which a USB drive is plugged will have a Java runtime environment of some kind installed.