This not only true of programming contest, but design contest.
Several years ago (in the 80s) a civil engineer friend entered an attraction blueprint contest sponsored by Disney. He did not won, but they use his blueprints to make an attraction anyway, without paying him nothing, or even placing a plaque or something that he could use to say, I made the blueprints of this. The catch as that when entering the contest he didn't notice in the small print that ALL enterings became property of Disney.
The lesson here, be sure to read the fine print before entering a contest.