  This paper proposes a novel, non-linear collusion attack on digital
fingerprinting systems. The attack is proposed for fingerprinting systems with
finite alphabet but can be extended to continuous alphabet. We analyze the
error probability of the attack for some classes of proposed random and
deterministic schemes and obtain a bound on the number of colluders necessary
to correctly estimate the host signal. That is, it requires fewer number of
colluders to defeat the fingerprinting scheme. Our simulation results show that
our attack is more powerful in practice than predicted by the theoretical
bound.
