A virus is a microscopic organism that can replicate only inside the cells of a host organism. Most viruses are so tiny they are only observable with at least a conventional optical microscope.
Recognized by the Guiness Book of World Records as the MMO with the longest play time per player, and easily the oldest game on this list (launching four years ahead of World of Warcraft, way back in 2001), Runescape deserves mention because it's one of the most updated and popular games of any kind on the planet.
Doctor Who - 53 (1963 to present) The longest-running scripted non-soap of all time is still going strong today. The TARDIS may have been lost in time and space for several years until its return in 2005, but it's remarkable that such a complex and cult series is still popular in 2016.