Bioterrorism is terrorism involving the intentional release or dissemination of biological agents like bacteria, viruses, or toxins, and may be in a naturally occurring or a human-modified form. Biological agents spread through the air, water, or in food. Some can also spread from person to person and very hard to detect. Anthrax, botulism, Ebola and other haemorrhagic fever viruses, plague, or smallpox could be used as biological agents. Biodefense uses medical measures to protect people against bioterrorism, includes medicines and vaccinations. It also includes medical research and preparations to defend against bioterrorist attacks.