  The amount of detected baryons in the local Universe is at least a factor of
two smaller than measured at high redshift. It is believed that a significant
fraction of the baryons in the current Universe is "hiding" in a hot
filamentary structure filling the intergalactic space, the Warm-Hot
Intergalactic Medium ($WHIM$). We found evidence of the missing baryons in the
$WHIM$ by detecting their signature on the angular correlation of diffuse X-ray
emission with the XMM-Newton satellite. Our result indicates that $(12\pm 5)$%
of the total diffuse X-ray emission in the energy range 0.4-0.6 keV is due to
intergalactic filaments. The statistical significance of our detection is
several sigmas ($\chi ^2>136$ N=19). The error bar in the X-ray flux is
dominated, instead, by cosmic variation and model uncertainties.
