1. A method for estimating an identity of a user of a computing system, the method comprising: an act of estimating environment-specific alterations of a received user sound that is received at the computing system; an act of facilitating a formulation of an expected audio model of a user's sound when a corresponding user-dependent audio model is subject to the estimated environment-specific alterations; an act of obtaining a comparison result of comparing the received user sound with the formulation of the expected audio model; and an act of estimating whether the user corresponding to the user-dependent audio model is the same as the user that emitted the user sound based on the comparison result, the user-dependent audio model being stored in a multi-system store.