Suppose you didn’t have to worry that the sensitive email you’re writing might land on the desk of your competitor. Or in the file of his company’s lawyer. Or on the front page of The New York Times.

There’s a service that offers this peace of mind—not in the future but right now. You sit at your computer and write a message much as you already do every day. But the program you use is special. When you receive a message, you click on it and before you can even read the text, the name, date, and subject disappear. Then you open the message, and when you reply or exit, it, too, vanishes. It’s the Cheshire cat of electronic communications.