  We present recent work on the Spectra of IceCube Neutrino (SIN) candidate
sources project. We defined a selection of candidate neutrino sources by
identifying blazars in the vicinity of IceCube's highest-energy neutrinos. We
now want to shed light on these source candidates' nature, starting at their
redshift, continuing with their black hole masses, their variability, and, for
the first time, a combined photon-neutrino spectral energy distribution. We
present their hybrid spectral energy distributions (combining photon and
neutrino fluxes), investigate the sources' variability in the near-infrared,
optical, X-ray, and $\gamma$-ray bands, and compare the variability with a
blazar sample of non-candidate sources. Furthermore, we search for flares at
the arrival time of the high-energy neutrinos.
