  We measured the extragalactic 0.7 keV X-ray background by observing the X-ray
shadow of a neutral gas cloud in the Magellanic Bridge region. Two \rosat PSPC
observations of total 104~ks were complemented by a detailed H I mapping of the
cloud with both the Parkes 64~m telescope and the Australia Telescope Compact
Array. From the detected anti-correlation between the observed background
intensity and the \ion{H}{1} column density of the cloud, we derived the
unabsorbed extragalactic background intensity as 28 keV s^{-1} cm^{-2} keV^{-1}
sr^{-1} at 0.7~keV. The 95% confidence lower limit 18 keV s^{-1} cm^{-2} keV^
{-1} sr^{-1}} is greater than the expected point-like source contribution < 14
keV s^{-1} cm^{-2} keV^{-1} sr^{-1}, constrained by the mean source spectrum
together with the total background intensity in the 1-2 keV band. A significant
fraction of the 0.7 keV background likely arises in a diffuse hot intergalactic
medium of a few million degrees, as has been predicted in hydrodynamic
simulations of cosmological structure formation.
