The BeppoSAX High Energy Large Area Survey ( HELLAS ) has surveyed about 85 deg ^ { 2 } of sky in the 5–10 keV band down to a flux of 4 - 5 \times 10 ^ { -14 } { erg~ { } cm } ^ { -2 } ~ { } { s } ^ { -1 } .
The source surface density of 16.9 \pm 6.4 deg ^ { -2 } at the survey limit corresponds to a resolved fraction of the 5–10 keV X–ray background ( XRB ) of the order of 20–30 % .

Hardness ratios analysis indicates that the spectra of a substantial fraction of the HELLAS sources ( at least one third ) are harder than a \alpha _ { E } = 0.6 power law .
This hardness may be due to large absorbing columns .
The hardness ratio analysis also indicates that many HELLAS sources may have a spectrum more complex than a single absorbed power law .
A soft component , superimposed to a strongly cut-off power law , is likely to be present in several sources .