OK how about this, (not my idea) Consider SETI.   
   Assume the aliens also know Shannon's theorem.   
   If they are communicating across the stars then they are most likely using a   
   wide bandwidth spread spectrum type technique.  And with a wide enough   
   bandwidth the signal will just look like noise to an outside observer.   
   Perhaps SETI is hopeless, at least in its current incarnation.   
      
   Horowitz at Harvard is involved with this. I would expect that they have   
   thought of spread spectrum. no? Searching for a ss signal would be interesting   
   - variables of frequency and bit pattern. Not as difficult as it sounds, imo.   
      
   jb   
      
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