  The atmospheric neutrino flux includes a component from the prompt decay of
charmed hadrons that becomes significant only at $E\ge 10$ TeV. At these
energies, however, the diffuse flux of cosmic neutrinos discovered by IceCube
seems to be larger than the atmospheric one. Here we study the possibility to
detect a neutrino interaction in down-going atmospheric events at km$^3$
telescopes. The neutrino signal will always appear together with a muon bundle
that reveals its atmospheric origin and, generically, it implies an increase in
the detector activity with the slant depth. We propose a simple algorithm that
could separate these events from regular muon bundles.
