  We consider a model for the reionization history of the Universe in which a
significant fraction of the observed optical depth is a result of direct
reionization by the decay products of a scaling cosmic defect network. We show
that such network can make a significant contribution to the reionization
history of the Universe even if its energy density is very small (the defect
energy density has to be greater than about $10^{-11}$ of the background
density). We compute the Cosmic Microwave Background temperature, polarization
and temperature-polarization cross power spectrum and show that a contribution
to the observed optical depth due to the decay products of a scaling defect
network may help to reconcile a high optical depth with a low redshift of
complete reionization suggested by quasar data. However, if the energy density
of defects is approximately a constant fraction of the background density then
these models do not explain the large scale bump in the
temperature-polarization cross power spectrum observed by WMAP.
