  I summarize the recent advances in determining the effects of
self-annihilating WIMP dark matter on the modification of the recombination
history, at times earlier than the formation of astrophysical objects.
Depending on mass and self-annihilation cross section, WIMP DM can reproduce
sizable amounts of the total free electron abundance at z > 6; as known, this
affects the CMB temperature and polarization correlation spectra, and can be
used to place stringent bounds in the particle mass vs cross-section plane.
WMAP5 data already strongly disfavor the region capable to explain the recent
cosmic positron and electrons anomalies in terms of DM annihilation, whereas in
principle the Planck mission has the potential to see a signal produced by a
candidate laying in that region, or from WIMPs with thermal annihilation
cross-sections <sv>=3e-26 cm3/s and masses below 50 GeV.
