Prior to widespread use of radio, popular "corridos" were passed around as an oral tradition, often to spread news of events (for example, "La cárcel de Cananea") and popular heroes and humor to the population, many of whom were illiterate prior to the post-Revolution improvements to the educational system. Academic study of "corridos" written during the Revolution shows that they were used as a means to communicate news throughout Mexico as a response to the propaganda being spread in the newspapers which were owned by the corrupt government of Porfirio Díaz. Sheet music of popular "corridos" was sold or included in publications. Other "corrido" sheets were passed out free as a form of propaganda, to eulogize leaders, armies, and political movements, or in some cases to mock the opposition. The best known Revolutionary "corrido" is "La Cucaracha", an old song that was rephrased to celebrate the exploits of Pancho Villa's army and poke fun at his nemesis Victoriano Huerta.