  We present a three-loop model of neutrino mass whose most-general Lagrangian
possesses a softly-broken accidental $Z_2$ symmetry. In the limit that a single
parameter vanishes, $\lambda\rightarrow0$, the $Z_2$ symmetry becomes exact and
the model contains a stable dark-matter candidate. However, even for finite
$\lambda\ll1$, long-lived dark matter is possible, giving a unified solution to
the neutrino mass and dark matter problems that does not invoke a new symmetry.
Taken purely as a neutrino mass model, the new physics can be at the TeV scale.
When dark matter is incorporated, however, only a singlet scalar can remain
this light, though the dark matter can be tested in direct-detection
experiments.
