  We add fermions to an abelian-gauged hidden sector. We show that the lightest
can be the dark matter with the right thermal relic abundance, and discovery is
within reach of upcoming dark matter detectors. We also show that these
fermions change Higgs boson phenomenology at the Large Hadron Collider (LHC),
and in particular could induce a large invisible width to the lightest Higgs
boson state. Such an invisibly decaying Higgs boson can be discovered with good
significance in the vector boson fusion channel at the LHC.
