  The existence of a quantum percolation threshold p_q<1 in the 2D quantum
site-percolation problem has been a controversial issue for a long time. By
means of a highly efficient Chebyshev expansion technique we investigate
numerically the time evolution of particle states on finite disordered square
lattices with system sizes not reachable up to now. After a careful finite-size
scaling, our results for the particle's recurrence probability and the
distribution function of the local particle density give evidence that indeed
extended states exist in the 2D percolation model for p<1.
