  We study an effective field theory which includes the Standard Model extended
by a Dark Sector consisting of two fermionic $SU(2)_{L}$-doublets. A $Z_2$
parity guarantees that, after electroweak symmetry breaking, the lightest
neutral particle is stable, acting as a WIMP. The dark sector interacts with
the Higgs and gauge bosons through renormalizable and non-renormalizable $d=5$
operators. We find that a WIMP with a mass around the electroweak scale, i.e.
accessible at the LHC, is consistent with collider and astrophysical data only
when non-trivial magnetic dipole interactions with the gauge bosons exist.
