A birthday present every eleven wallets? The security of customer-chosen banking PINs Joseph Bonneau, Sören Preibusch, Ross Anderson Computer Laboratory University of Cambridge {jcb82,sdp36,rja14}@cl.cam.ac.uk Abstract. We provide the first published estimates of the difficulty of guessing a human-chosen 4-digit PIN. We begin with two large sets of 4-digit sequences chosen outside banking for onl