  Effective defense against cyber-physical attacks in power grid requires the
capability of accurate damage assessment within the attacked area. While some
solutions have been proposed to recover the phase angles and the link status
(i.e., breaker status) within the attacked area, existing solutions made the
limiting assumption that the grid stays connected after the attack. To fill
this gap, we study the problem of recovering the phase angles and the link
status under a general cyber-physical attack that may partition the grid into
islands. To this end, we (i) show that the existing solutions and recovery
conditions still hold if the post-attack power injections in the attacked area
are known, and (ii) propose a linear programming-based algorithm that can
perfectly recover the link status under certain conditions even if the
post-attack power injections are unknown. Our numerical evaluations based on
the Polish power grid demonstrate that the proposed algorithm is highly
accurate in localizing failed links once the phase angles are known.
