Guest Editors' Introduction: Secure or Usable?

There's an old joke that computers are actually easy machines to secure: just turn them off, lock them in a metal-lined room, and throw away the key. What you end up with is a machine that is very secure--just not very usable.As the joke's continuing popularity demonstrates, many people believe that there is an inherent trade-off between security and usability. A computer without passwords is usable, but not very secure. On the other hand, a computer that requires you to authenticate every 5 minutes with your password and a fresh drop of blood might indeed be very secure, but nobody would want to use it.