How do they make them available only to teachers? I don't know about the databases, but I know you can buy teacher's editions of textbooks online legitimately,

How do they make them available only to teachers? I don't know about the databases, but I know you can buy teacher's editions of textbooks online legitimately, like through Amazon. I also know that last time one of my (student edition) textbooks came with online material, access was restricted by requiring you to enter a code printed in the book. Even if the teachers' resources are secured better than that, it must be nearly impossible to prevent all of their customers from posting those questions online -- most of my profs post assignments online rather than giving out hard copies because it is just more convenient for both them and us this way. Some of those questions come from the textbook; I don't know how many come from some other teachers' resource. I know I've stumbled upon other profs using some of the same questions, and sometimes even answer keys, because I Googled some terminology I didn't understand which was apparently unique to that publisher.