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.
01 January 2009. The Ultima franchise is the longest-running RPG series, at 29 years. Ultima I: The First Age of Darkness was released in 1980 while the most recent entry to the series, Ultima Online: The Stygian Abyss, came out in 2009.