  The BeppoSAX High Energy Large Area Survey (HELLAS) has surveyed several tens
of square degrees of the sky in the 5--10 keV band down to a flux of about 5
10^-14 erg cm-2 s-1. The extrapolation of the HELLAS logN--logS towards fainter
fluxes with an euclidean slope is consistent with the first XMM measurements,
in the same energy band, which are a factor 20 more sensitive. The source
counts in the hardest band so far surveyed by X-ray satellites are used to
constrain XRB models. It is shown that in order to reproduce the 5--10 keV
counts over the range of fluxes covered by BeppoSAX and XMM a large fraction of
highly absorbed (logN_H = 23--24 cm-2), luminous (L_X > 10^44 erg s-1) AGN is
needed. A sizeable number of more heavily obscured, Compton thick, objects
cannot be ruled out but it is not required by the present data. The model
predicts an absorption distribution consistent with that found from the
hardness ratios analysis of the so far identified HELLAS sources. Interestingly
enough, there is evidence of a decoupling between X-ray absorption and optical
reddening indicators especially at high redshifts/luminosities where several
broad line quasars show hardness ratios typical of absorbed power law models
with logN_H=22--24 cm-2.
