  We present a spectroscopic study of 41 hard X-ray sources detected
serendipitously with high significance (> 5 sigma in the 2-10 keV band) in
seven EPIC performance/verification phase observations. The large collecting
area of EPIC allows us to explore the spectral properties of these faint hard
X-ray sources with 2< F_{2-10} < 80 x 10^{-14} erg cm^{-2}s^{-1} even though
the length of the exposures are modest (~ 20 ks). Optical identifications are
available for 21 sources of our sample. Using a simple power law plus Galactic
absorption model we find an average value of the photon index Gamma ~ 1.6-1.7,
broadly consistent with recent measurements made at similar fluxes with ASCA
and with Chandra stacked spectral analyses. We find that 31 out of 41 sources
are well fitted by this simple model and only eight sources require absorption
in excess of the Galactic value. Interestingly enough, one third of these
absorbed sources are broad line objects, though with moderate column densities.
Two sources in the sample are X-ray bright optically quiet galaxies and show
flat X-ray spectra. Comparing our observational results with those expected
from standard synthesis models of the cosmic X-ray background (CXB) we find a
fraction of unabsorbed to absorbed sources larger than predicted by theoretical
models at our completeness limit of F_{2-10} ~ 5 x 10^{-14} erg cm^{-2}s^{-1}.
The results presented here illustrate well how wide-angle surveys performed
with EPIC on board XMM-Newton allow population studies of interesting and
unusual sources to be made as well as enabling constraints to be placed on some
input parameters for synthesis models of the CXB.
