  There is strong support in favor of an unusual $s_{\pm}$ superconducting
state in the new iron-based superconductors, in which the gap parameter has
opposite signs in different bands. In this case scattering between different
bands by impurities has a pair-breaking effect and introduces states inside the
gap. We studied the statistics of disorder-induced subgap states in $s_{\pm}$
superconductors due to collective effects of impurities. Numerically solving
the two-band Bogolyubov equations, we explored the behavior of the density of
states and localization length. We located the mobility edge separating the
localized and delocalized states for the 3D case and the crossover between the
weak and strong localization regimes for the 2D case. We found that the widely
used self-consistent T-matrix approximation is not very accurate in describing
subgap states.
