"A fascinating dialogue is developing between psychologists and security engineers. At the macro scale, societal overreactions to terrorism are founded on the misperception of risk and uncertainty, which has deep psychological roots. At the micro scale, more and more crimes involve deception; as security engineering gets better, it's easier to mislead people than to hack computers or hack through walls. Many systems also fail because of usability problems: the designers have different mental models of threats and protection mechanisms from users. Wrong assumptions about users can lead systems to discriminate against women, the less educated and the elderly. And misperceptions cause security markets to fail: many users buy snake oil, while others distrust quite serviceable mechanisms. Security is both a feeling and a reality, and they're different. The gap gets ever wider, and ever more important."