Curse of the Secret Question
It appears that Paris Hilton's Sidekick was hacked becuase her secret question was "What's your favorite pet's name?" The answer, of course, was her dog, Tinkerbell, who is almost as famous as she is.
This is what Bruce Schneier has called the "curse of the secret question":
It's happened to all of us: We sign up for some online account, choose a difficult-to-remember and hard-to-guess password, and are then presented with a "secret question" to answer. Twenty years ago, there was just one secret question: "What's your mother's maiden name?" Today, there are more: "What street did you grow up on?" "What's the name of your first pet?" "What's your favorite color?" And so on.
The point of all these questions is the same: a backup password. If you forget your password, the secret question can verify your identity so you can choose another password or have the site e-mail your current password to you. It's a great idea from a customer service perspective -- a user is less likely to forget his first pet's name than some random password -- but terrible for security. The answer to the secret question is much easier to guess than a good password, and the information is much more public. (I'll bet the name of my family's first pet is in some database somewhere.) And even worse, everybody seems to use the same series of secret questions.
The result is the normal security protocol (passwords) falls back to a much less secure protocol (secret questions). And the security of the entire system suffers.
Technorati tag: security