  We consider a model of dark matter whose most prominent signature is a
monochromatic flux of TeV neutrinos from the galactic center. As an example of
a general scenario, we consider a specific model where the dark matter is a
fermion in the adjoint representation of a hidden SU(N) gauge group that
confines at GeV energies. The absence of light fermionic states in the dark
sector ensures stability of dark matter on cosmological time scales. Dark
matter couples to the standard model via the neutrino portal, that is, the
singlet operator H L constructed from the Higgs and lepton doublets, which is
the lowest dimensional fermionic singlet operator in the standard model. This
coupling prompts dark matter decay where the dominant decay channel has one
neutrino (and at least one dark glueball) in the final state. Other decay
channels with charged standard model particles involve more particles in the
final state and are therefore suppressed by phase space. In consequence, the
standard indirect detection signals like gamma-ray photons, antiprotons and
positrons are suppressed with respect to the neutrino signal. This coupling via
the neutrino portal is most robustly constrained by Super-Kamiokande, which
restricts the dark matter lifetime to be larger than 10^25 seconds. In the near
future, the scenario will be probed by the new generation of neutrino
telescopes. ANTARES will be sensitive to a dark matter lifetime of order 10^26
seconds, while IceCube/DeepCore can probe a lifetime as large as 10^27 seconds.
