This article examines issues in the assumption of equal contributions in digital fingerprinting.
With a digital fingerprinting scheme, a vendor of digital copies of copyrighted material marks each individual copy with a unique fingerprint. If an illegal copy appears, it can be traced back to one or more guilty pirates due to this fingerprint. A coalition of pirates may combine their copies to produce an unauthorized copy with a false, hybrid fingerprint. It is often assumed in the literature that the members of the collusion will make equal contributions to the hybrid fingerprint, because nobody will accept an increased risk of being caught. The authors of this article argue that no such assumption is valid a priori, and that a published solution by Sebe and Domingo-Ferrer can be broken by breaking the assumption. (Publisher abstract provided)