  We extend the validity of Hardy's nonlocality without inequalities proof to
cover the case of special one-parameter classes of non-pure statistical
operators. These mixed states are obtained by mixing the Hardy states with a
completely chaotic noise or with a colored noise and they represent a realistic
description of imperfect preparation processes of (pure) Hardy states in
nonlocality experiments. Within such a framework we are able to exhibit a
precise range of values of the parameter measuring the noise affecting the
non-optimal preparation of an arbitrary Hardy state, for which it is still
possible to put into evidence genuine nonlocal effects. Equivalently, our work
exhibits particular classes of bipartite mixed states whose constituents do not
admit any local and deterministic hidden variable model reproducing the quantum
mechanical predictions.
