  The search for heavily obscured active galactic nuclei (AGNs) has been
revitalized in the last five years by NuSTAR, which has provided a good census
and spectral characterization of a population of such objects, mostly at low
redshift, thanks to its enhanced sensitivity above 10 keV compared to previous
X-ray facilities, and its hard X-ray imaging capabilities. We aim at
demonstrating how NGC2785, a local (z=0.009) star-forming galaxy, is
responsible, in virtue of its heavily obscured active nucleus, for significant
contamination in the non-imaging BeppoSAX/PDS data of the relatively nearby
(~17 arcmin) quasar IRAS 09104+4109 (z=0.44), which was originally
mis-classified as Compton thick. We analyzed ~71 ks NuSTAR data of NGC2785
using the MYTorus model and provided a physical description of the X-ray
properties of the source for the first time. We found that NGC2785 hosts a
heavily obscured (NH~3*10^{24} cm^{-2}) nucleus. The intrinsic X-ray luminosity
of the source, once corrected for the measured obscuration (L(2-10 keV)~10^{42}
erg/s), is consistent within a factor of a few with predictions based on the
source mid-infrared flux using widely adopted correlations from the literature.
Based on NuSTAR data and previous indications from the Neil Gehrels Swift
Observatory (BAT instrument), we confirm that NGC2785, because of its hard
X-ray emission and spectral shape, was responsible for at least one third of
the 20-100 keV emission observed using the PDS instrument onboard BeppoSAX,
originally completely associated with IRAS 09104+4109. Such emission led to the
erroneous classification of this source as a Compton-thick quasar, while it is
now recognized as Compton thin.

High Energy Astrophysical Phenomena