Compounds, methods and pharmaceutical compositions for treating viral infections, by administering certain novel semicarbazides, sulfonyl carbazides, ureas and related compounds in therapeutically effective amounts are disclosed. Methods for preparing the compounds and methods of using the compounds and pharmaceutical compositions thereof are also disclosed. In particular, the treatment and prophylaxis of viral infections such as caused by hemorrhagic fever viruses is disclosed, i.e., including but not limited to Arenaviridae (Junin, Machupo, Guanavito, Sabia and Lassa), Filoviridae (ebola and Marburg viruses), Flaviviridae (yellow fever, omsk hemorrhagic fever and Kyasanur Forest disease viruses), and Bunyaviridae (Rift Valley fever).