  As the electromagnetic gauge symmetry makes the electron stable, a new
abelian gauge symmetry may be responsible for the stability of superheavy dark
matter. The gauge boson associated with the new gauge symmetry naturally plays
the role of dark radiation and contributes to the effective number of `neutrino
species', which has been recently measured by Planck. We estimate the
contribution of dark radiation from the radiative decay of a scalar particle
induced by the WIMPZILLA in the loop. The scalar particle may affect the
invisible decay of the Higgs boson by the Higgs portal type coupling.
