  The connection between the sub-mm and the hard X-ray backgrounds is studied
by comparing data at 2-10 keV and at 850um for a sample of 34 sources at fluxes
(or limiting fluxes) which resolve most of the background in the two bands.
These data were obtained with new SCUBA observations and by correlating data
sets available from the literature. None of the 11 hard X-ray (2-10 keV)
sources has a counterpart at 850um, with the exception of a faint Chandra
source, which is a candidate type 2 QSO at high redshift. These data indicate
that 2-10 keV sources brighter than 10^-15 erg s-1 cm-2, which make at least
75% of the background in this band, contribute for less than 7% to the
submillimetric background. Out of the 24 SCUBA sources 23 are undetected by
Chandra. These data indicate that most of these SCUBA sources must be powered
either by starburst activity, or by an AGN which is obscured by a column Nh >
10^25 cm-2, with a reflection efficiency in the hard X-rays significantly lower
than 1% in most cases.
