  MACHOs (Massive Astrophysical Compact Halo Objects) - as discovered by
microlensing experiments towards the LMC - provide a natural explanation for
the galactic halo dark matter. A realistic possibility is that MACHOs are brown
dwarfs of mass $\sim 0.1 M_{\odot}$. Various arguments suggest that brown
dwarfs should have a coronal X-ray emission of $\sim 10^{27}$ erg s$^{-1}$. As
MACHOs are presumably clumped into dark clusters (DCs), each DC is expected to
have a total X-ray luminosity of $\sim 10^{29}-10^{32}$ erg s$^{-1}$. We
discuss the possibility that dark clusters contribute to the diffuse X-ray
background (XRB) or show up as discrete sources in very deep field X-ray
satellite observations. Moreover, from the observed diffuse XRB we infer that
the amount of virialized diffuse gas present in the galactic halo can at most
make up 5% of the halo dark matter.
