  In this paper we review the properties of the black hole entropy in the light
of a general conformal field theory treatment. We find that the properties of
horizons of the BTZ black holes in ADS_{3}, can be described in terms of an
effective unitary CFT_{2} with central charge c=1 realized in terms of the
Fubini-Veneziano vertex operators.
  It is found a relationship between the topological properties of the black
hole solution and the infinite algebra extension of the conformal group in 2D,
SU(2,2), i.e. the Virasoro Algebra, and its subgroup SL(2,Z) which generates
the modular symmetry. Such a symmetry induces a duality for the black hole
solution with angular momentum J\neq 0. On the light of such a global symmetry
we reanalyze the Cardy formula for CFT_{2} and its possible generalization to
D>2 proposed by E. Verlinde.
