 However, other sources state that Gruber became involved in a prolonged legal battle to recover the rights to the music he had written and that had been lifted (unknowingly or not) by Sousa and widely sold by sheet music publishers who reaped profits while Gruber received nothing.The music became so popular that it was also used in radio ads by firms such as the Hoover Vacuum Company.Gruber's position was rejected by the courts, which ruled that he had waited too long to complain and that his music was by that time in the public domain.