  A number of theories, spanning a wide range of mass scales, predict dark
matter candidates that have lifetimes much longer than the age of the universe,
yet may produce a significant flux of gamma rays in their decays today. We
constrain such late decaying dark matter scenarios model-independently by
utilizing gamma-ray line emission limits from the Galactic Center region
obtained with the SPI spectrometer on INTEGRAL, and the determination of the
isotropic diffuse photon background by SPI, COMPTEL and EGRET observations. We
show that no more than ~5% of the unexplained MeV background can be produced by
late dark matter decays either in the Galactic halo or cosmological sources.
