Conformal nature of the Hawking radiation

String theory usually represents quantum black holes as systems whosestatistical mechanics reproduces Hawking's thermodynamics in a very satisfactory way. Complicated brane theoretical models are worked out, as quantum versions of Supergravity solutions. These models are then assumed to be in thermal equilibrium: this is a little cheating, because one is looking for an explanation of the seeming thermodynamical nature of black holes, so these cannot be assumed to be nite temperature systems! In the model presented here, the black body spectrum arises with no statistical hypothesis as an approximation of the unitary evolution of microscopic black holes, which are always described by a 1 + 1 conformal eld theory, characterized by some Virasoro algebra. At the end, one can state that the Hawking-thermodynamics of the system is a by-product of the algebraic Virasoro -symmetric nature of the event horizon.This is the central result of the present work.