In this essay, written for a symposium on surveillance for the University of Chicago Law Review, I examine some common difficulties in the way that liberty is balanced against security in the context of data mining. Countless discussions about the trade-offs between security and liberty begin by taking a security proposal and then weighing it against what it would cost our civil liberties. Often, the liberty interests are cast as individual rights and balanced against the security interests, which are cast in terms of the safety of society as a whole. Courts and commentators defer to the government's assertions about the effectiveness of the security interest. In the context of data mining, the liberty interest is limited by narrow understandings of privacy that neglect to account for many privacy problems. As a result, the balancing concludes with a victory in favor of the security interest. But as I argue, important dimensions of data mining's security benefits require more scrutiny, and the privacy concerns are significantly greater than currently acknowledged. These problems have undermined the balancing process and skewed the results toward the security side of the scale.