  Atmospheric neutrinos are produced in air showers, when cosmic ray primaries
hit the Earth's atmosphere and interact hadronically. The conventional neutrino
flux, which dominates the neutrino data measured in the GeV to TeV range by
neutrino telescopes, is produced by the decay of charged pions and kaons.
Prompt atmospheric neutrinos are produced by the decay of heavier mesons
typically containing a charm quark. Their production is strongly suppressed,
but they are expected to exhibit a harder energy spectrum. Hence, they could
dominate the atmospheric neutrino flux at energies above ~ 100 TeV. Such a
prompt atmospheric flux component has not yet been observed. Therefore, it is
an interesting signal in a diffuse neutrino search, but also a background in
the search for a diffuse astrophysical neutrino flux. The sensitivity of
diffuse neutrino searches with the IceCube Neutrino observatory has reached the
level of theoretical expectations of prompt neutrino fluxes, and recent results
are presented.
