  In the past years a wealth of observations allowed to unravel the structural
properties of the Dark Matter Halos around spirals. First, their rotation
curves follow an Universal profile (URC) that can be described in terms of an
exponential thin stellar disk and a dark halo with a constant density core,
whose relative importance increases with galaxy luminosity. Careful studies of
individual objects reveal that dark halos have a core, whose size $r_0$
correlates with the central density $\rho_0$.
  These properties are in serious discrepancy with the cuspy density
distribution predicted by N-body simulations in collisionless $\Lambda$CDM
Cosmology.
