  The injection of secondary particles produced by Dark Matter (DM)
annihilation around redshift 1000 would inevitably affect the process of
recombination, leaving an imprint on Cosmic Microwave Background (CMB)
anisotropies and polarization. We show that the most recent CMB measurements
provided by the WMAP satellite mission place interesting constraints on DM
self-annihilation rates, especially for models that exhibit a large Sommerfeld
enhancement of the annihilation cross-section, as recently proposed to fit the
PAMELA and ATIC results. Furthermore, we argue that upcoming CMB experiments
such as Planck, will improve the constraints by at least one order of
magnitude, thus providing a sensitive probe of the properties of DM particles.
