  As-vacancies (V_As) in La-1111-systems, which are nominally non-magnetic
defects, are shown to create in their vicinity by symmetry ferromagnetically
oriented local magnetic moments due to the strong, covalent bonds with
neighboring Fe atoms that they break. From microscopic theory in terms of an
appropriately modified Anderson-Wolff model, we find that the moment formation
results in a substantially enhanced paramagnetic susceptibility in both the
normal and superconducting (SC) state. Despite the V_As act as magnetic
scatterers, they do not deteriorate SC properties which can even be improved by
V_As by suppressing a competing or coexisting commensurate spin density wave or
its remnant fluctuations. Due to the induced local magnetic moments an
s_++-scenario in related systems is unlikely.
