User blog comment:Argorrath/Treyarch posts a message of zombies; possibly hinting to a DLC 4/@comment-71.197.43.36-20130805144538/@comment-25496444-20130807121520

They would give at least an implication of what their source is, such as an employee of Treyarch but not giving any names, but not mentioning anything is not the only way of keeping a secret.