  A theory input is needed for the estimation of the largest background for the
$H\rightarrow WW$ search at the LHC. This is the shape of the $m_{\ell\ell}$
spectrum from continuum $WW$ production. We find this to depend on how NLO
matrix elements are merged with parton showers, and we compare the results from
a number of different implementations. The results suggest that both the size
of the background estimate and its uncertainty may have been underestimated.
This conclusion is reinforced by a "Note Added", which comments on the LHC
results released on November 14 2012.
