This paper presents a theoretical security analysis of lattice data hiding. The security depends on the secrecy of a dither signal that randomizes the codebook. If the same secret dither is used for watermarking multiple objects, an attacker can exploit the information leakage inherent to the lattice data hiding scheme in order to compute an estimate of the dither. Our analysis is aimed at measuring in an information-theoretic sense the amount of information that leaks from each watermarked signal, emphasizing the role of the embedding lattice on the achievable security level. The information leakage determines in a natural way the lowest dither estimation error attainable, which can be taken into account for design criteria. A comparison with spread spectrum methods in terms of security is also given. Categories and Subject Descriptors D.2.11 [Software Engineering]: Software Architectures— information hiding General Terms Theory, Security Keywords Watermarking security, equivocatio...