  The Planck and WMAP9 satellites, as well as the ATACAMA and South Pole
telescopes, have recently presented results on the angular power spectrum of
the comic microwave background. Data tentatively point to the existence of an
extra radiation component in the early universe. Here, we show that this extra
component can be mimicked by ordinary WIMP dark matter particles whose majority
is cold, but with a small fraction being non-thermally produced in a
relativistic state. We present a few example theories where this scenario is
explicitly realized, and explore the relevant parameter space consistent with
BBN, CMB and Structure Formation bounds.
