1. A method for preserving privacy of one-dimensional nonstationary data streams, the method comprising: receiving a one-dimensional nonstationary data stream; calculating, for a given instant of sub-space of time, a set of first-moment statistical values for the data wherein the first moment statistical values include a principal component for the sub-space of time; and perturbing the data with noise along the principal component in proportion to the first-moment of statistical values so that at least part of a set of second-moment statistical values for the data is perturbed by the noise only within a predetermined variance.