  We briefly report on an on-going spectroscopic study of hard X-ray sources
selected serendipitously in 12 XMM-Newton fields. Results for the analysis of
the 41 sources from the first seven EPIC observations have been discussed in a
previous paper (Piconcelli et al. 2002, Paper I) where we found an absolute
fraction of X-ray absorbed sources (~30%) lower than expected (~50%) by the
predictions of popular CXB synthesis models at F(2-10)~5x10**(-14) erg cm**-2
s**-1. We present here the preliminary results concerning the whole sample
including five new deeper XMM-Newton measurements increasing the sample to 90
sources. Even if still on-going, the present study appears to confirm and
extend down to F(2-10)~10**(-14) erg cm**-2 s**-1 the above mismatch between
observational data and theoretical expectations regarding the fraction of
absorbed sources. Furthermore the sample average spectral index of 1.5-1.6 is
steeper than the CXB slope indicating that the majority of obscured sources
making the bulk of the CXB resides at even lower hard X-ray fluxes.
