Your mother's maiden name

At least three places/organizations I do business with ask for this bit of info as a "security check." The idea being, I think that you mother's maiden name is something that only those intimately familiar with your family would know, and therefore is an easy, universally applicable kind of "password" to be used before handing out sensitive info. But I've always wondered just how secure this "password" is. Recalling Eric Hughes statement that "cryptography is all economics," and realizing that someone with an unlimited budget could probably scrounge that info after some effort -- just how much effort would it take? And how secure is "mom's maiden name" as a password for obtaining sensitive information over the phone?