  High energy gamma-rays and neutrinos can be produced both by the annihilation
and by the possible slow decay of dark matter particles. We discuss the fluxes
and spectra of such secondaries produced by dark matter particles in the
universe and their observability in competition with other astrophysical
gamma-ray signals and with atmospheric neutrinos. To do this, we work within
the assumption that the dark matter particles are neutralinos which are the
lightest supersymmetric particles (LSPs) predicted by supersymmetry theory.
