  This paper presents the studies of the background contribution to the $H
\rightarrow 4l$ searches originating from the processes of off-shell (virtual)
photon emissions and their conversions into lepton pairs accompanying the
production of $Z/ \gamma ^*$-bosons at the LHC. They extend the analyses of the
irreducible background presented in the ATLAS and CMS Higgs papers by taking
into account the emissions of off-shell photons by parton showers. Including
these effects does not change significantly the Higgs-searches background
level, provided that the transverse momentum of each of the final-state leptons
is restricted to the range of $p_{T, l} > 7$ GeV. In the kinematical region
extended towards lower lepton transverse momenta the parton-shower contribution
becomes important. A measurement method for pinning down the parton-shower
effects is proposed.
