  We report analysis of high microlensing event MOA-2008-BLG-379, which has a
strong microlensing anomaly at its peak, due to a massive planet with a mass
ratio of q = 6.9 x 10^{-3}. Because the faint source star crosses the large
resonant caustic, the planetary signal dominates the light curve. This is
unusual for planetary microlensing events, and as a result, the planetary
nature of this light curve was not immediately noticed. The planetary nature of
the event was found when the MOA Collaboration conducted a systematic study of
binary microlensing events previously identified by the MOA alert system. We
have conducted a Bayesian analysis based on a standard Galactic model to
estimate the physical parameters of the lens system. This yields a host star
mass of M_L = 0.66_{-0.33}^{+0.29} M_Sun orbited by a planet of mass m_P =
4.8_{-2.4}^{+2.1} M_Jup at an orbital separation of a = 4.1_{-1.5}^{+1.9} AU at
a distance of D_L = 3.6 +/- 1.3 kpc. The faint source magnitude of I_S = 21.30
and relatively high lens-source relative proper motion of mu_rel = 7.6 +/- 1.6
mas/yr implies that high angular resolution adaptive optics or Hubble Space
Telescope observations are likely to be able to detect the source star, which
would determine the masses and distance of the planet and its host star.
