  Extending the standard model with three right-handed neutrinos ($N_k$) and a
second Higgs doublet ($\eta$), odd under the discrete parity symmetry $Z_2$,
Majorana neutrino masses can be generated at 1-loop order. In the resulting
model, the lightest stable particle, either a boson or a fermion, might be a
dark matter candidate. Here we assume a specific mass spectrum ($M_1\ll M_2 <
M_3 < m_\eta$) and derive its consequences for dark matter and collider
phenomenology. We show that (i) the lightest right-handed neutrino is a warm
dark matter particle that can give a $\sim$10% contribution to the dark matter
density; (ii) several decay branching ratios of the charged scalar can be
predicted from measured neutrino data. Especially interesting is that large
lepton flavour violating rates in muon and tau final states are expected.
Finally, we derive upper bounds on the right-handed neutrino Yukawa couplings
from the current experimental limit on $Br(\mu\to e\gamma)$.
