  Privacy Preserving Data Mining (PPDM) addresses the problem of developing
accurate models about aggregated data without access to precise information in
individual data record. A widely studied \emph{perturbation-based PPDM}
approach introduces random perturbation to individual values to preserve
privacy before data is published. Previous solutions of this approach are
limited in their tacit assumption of single-level trust on data miners.
  In this work, we relax this assumption and expand the scope of
perturbation-based PPDM to Multi-Level Trust (MLT-PPDM). In our setting, the
more trusted a data miner is, the less perturbed copy of the data it can
access. Under this setting, a malicious data miner may have access to
differently perturbed copies of the same data through various means, and may
combine these diverse copies to jointly infer additional information about the
original data that the data owner does not intend to release. Preventing such
\emph{diversity attacks} is the key challenge of providing MLT-PPDM services.
We address this challenge by properly correlating perturbation across copies at
different trust levels. We prove that our solution is robust against diversity
attacks with respect to our privacy goal. That is, for data miners who have
access to an arbitrary collection of the perturbed copies, our solution prevent
them from jointly reconstructing the original data more accurately than the
best effort using any individual copy in the collection. Our solution allows a
data owner to generate perturbed copies of its data for arbitrary trust levels
on-demand. This feature offers data owners maximum flexibility.
