An Ultraviolet host, or UV Host, is the ultimate in artificial reality. These rare hosts are able to simulate real life so effectively that it is difficult to differentiate between them and reality.
When a decker enters a UV host, his utilities will alter to appear as tools that apply to what they do. A decker can actually make use of his real world skills for actions inside the UV host, or use his computer ability at reduced effectiveness. Upon jacking out the decker will automatically experience a form of dumpshock caused by the system.
UV systems are extremely rare. The SCIRE system had UV hosts in it, and there are rumors about other UV's around the Matrix.