There is some evidence that the Japanese used anthrax as a biological weapon (BW) in China during World War II (Christopher GW, et al. Biological warfare: A historical perspective. JAMA 1997; 278 (Aug 6): 412-17).
Since then, several countries are believed to have incorporated anthrax spores into biological weapons. Intelligence analysts believe that at least seven potential adversaries have an offensive BW capability to deliver anthrax -- twice the number of countries when the 1972 Biological and Toxin Weapons Convention (BTWC) took effect. The BTWC was designed to prohibit such activity.
Iraq admitted to the United Nations in 1995 that it loaded anthrax spores into warheads during the Gulf War. In the post-cold war era, the former Soviet Union admitted to having enough anthrax on hand to kill every person on the planet several times over. The accidental aerosolized release of anthrax spores from a military microbiology facility in the former Soviet Union city of Sverdlovsk in 1979 resulted in at least 79 cases of anthrax infection and 68 human deaths and demonstrated the lethal potential of anthrax aerosols. Members of Aum Shinrikyo, the group responsible for the 1995 Tokyo sarin attack, reportedly experimented with biological agents in Japan before resorting to chemical agents. A lengthy article in the May 26, 1998, edition of the New York Times reported that members of Aum Shinrikyo released anthrax spores and botulinum toxin in Tokyo, Yokohama, and Yokosuka in 1990, targeting Japanese government and U.S. Navy facilities. Fortunately, no one was injured in these events.
Anthrax spores have also been used as a weapon inside the United States by unknown terrorists in the Fall of 2001. The attack killed 5 people and infected at least 17 others.