Machines like cars and toasters can malfunction and break down. However, we expect that no one has maliciously rigged our brakes to fail or our television to explode. It's difficult to engineer this type of sabotage. An attacker needs to break into a home or car to accomplish his task, exposing himself to detection and physical harm.

We expect society to protect us from harm, but also to insure our privacy. We assume that, for most people, the risks associated with violating another person's privacy outweigh the benefits. Our expectations about the privacy of our home, our car and our person are usually met. Or are they?

The hacker who invades a computer never needs to leave the comfort of her home. She may be virtually impossible to detect or trace. Everyone surely agrees that a hacker has no right to sneak into our computers. But, what if she's just building the software that could allow someone else to do it? Is there anything wrong with that?