From MSNBC:
Exactly 25 years ago, in the body of the world’s first diagnosed AIDS case, the full capabilities and mysterious workings of a virus unfolded. Three years later, in 1984, Luc Montagnier of the Pasteur Institute of Paris and Robert Gallo, then of the National Cancer Institute, announced their discovery of HIV, the virus that infects the human immune system and causes AIDS.
Even though the smallest viruses are only about one-millionth of an inch long, they live up to their Latin namesake — poison. They are capable of infecting and hijacking a human body, creating health hazards as minor as the common flu and as disastrous as the AIDS epidemic.Viruses are neatly organized, petite packages of genetic material, shaped like rods, filaments, harpoons, or spheres. Proteins surround the package, which is called a capsid. Some viruses have an added layer of lipids that coat the capsid. Little extensions on the virus are called antigens, which help the virus hunt down the target host cell.
More here.