  The dc-conductivity of electrons on a square lattice interacting with a local
repulsion in the presence of disorder is computed by means of quantum Monte
Carlo simulations. We provide evidence for the existence of a transition from
an Anderson insulator to a correlated disordered metal with a universal value
of the critical dc-conductivity \sigma_{dc,crit} = (1.18 \pm 0.06) e^{2}/h at
the transition.
