A malignant pustule is

Cutaneous anthrax: lesion stas as a papule 1-3 days after infection and becomes vesicular, containing a fluid which may be clear or bloodstained. The whole area is congested, edematous and several satellite lesions filled with serum or yellow fluid are arranged around a central necrotic lesion which is covered by a black eschar. This is a malignant pustule. The disease is used to be common in dock workers carrying loads of hides and skins on their bare backs and hence, was known as hide poers disease. Reference: Textbook of Microbiology; Anathanarayan and paniker's; 10th edition; Page no: 250