  We show that a collisionless shock necessarily forms during the shock
breakout of a supernova (SN) surrounded by an optically thick wind. An intense
non-thermal flash of <~ MeV gamma rays, hard X-rays and multi-TeV neutrinos is
produced simultaneously with and following the soft X-ray breakout emission,
carrying similar or larger energy than the soft emission. The non-thermal flash
is detectable by current X-ray telescopes and may be detectable out to 10's of
Mpc by km-scale neutrino telescopes.
