  Mid-IR colour selection techniques have proved to be very efficient in
finding AGN. This is because the AGN heats the surrounding dust producing warm
mid-IR colours. Using the WISE 3.6, 4.5 and 12 $\mu m$ colours, the largest
sample of IR selected AGN has already been produced containing 1.4 million AGN
over the whole sky. Here, we explore the X-ray properties of this AGN sample by
cross-correlating it with the subsample of the 3XMM X-ray catalogue that has
available X-ray spectra and at the same time optical spectroscopy from SDSS.
Our goal is to find rare luminous obscured AGN. Our final sample contains 65
QSOs with $\rm{log}\,\nu L_\nu \ge 46.2$\,erg\,s$^{-1}$. This IR luminosity cut
corresponds to $\rm{log}\,L_X \approx 45$\,erg\,s$^{-1}$, at the median
redshift of our sample ($z=2.3$), that lies at the bright end of the X-ray
luminosity function at $z>2$. The X-ray spectroscopic analysis reveals seven
obscured AGN having a column density $\rm N_H>10^{22} cm^{-2}$. Six of them
show evidence for broad [CIV] absorption lines and five are classified as
BALQSOs. We fit the optical spectra of our X-ray absorbed sources to estimate
the optical reddening. We find that none of these show any obscuration
according to the optical continuum. These sources add to the growing evidence
for populations of luminous QSOs with evidence for substantial absorption by
outflowing ionised material, similar to those expected to be emerging from
their absorbing cocoons in the framework of AGN/galaxy co-evolution.
