  Most of the energy of the X-ray background is contributed by sources with a
hard X-ray spectrum, harder than the spectrum observed in nearby type 1 AGNs.
The hard background contributors are conventionally identified with type 2
AGNs, obscured by circumnuclear matter both in the optical and in the soft X
rays. However, preliminary results of identification programs seem to find
systematically few type 2 AGNs in samples selected with obscuration insensitive
criteria. We discuss this issue, and assess the various scenarios which are
being proposed to solve the discrepancy.
