Topological defects and cosmic microwave background anisotropies: Are the predictions reliable ?

We consider a network of topological defects which can partly decay into neutrinos, photons, baryons, or cold dark matter. We find that the degree-scale amplitude of the cosmic microwave background anisotropies as well as the shape of the matter power spectrum can be considerably modified when such a decay is taken into account. We conclude that present predictions concerning structure formation by defects might be unreliable.