"Core War (or Core Wars) is a programming game in which two or more battle programs (called warriors) compete for the control of the MARS virtual computer (Memory Array Redcode Simulator). These battle programs are written in an abstract assembly language called Redcode. The object of the game is to cause all processes of the opposing program(s) to terminate, leaving your program in sole possession of the machine.
...The game was introduced to the public in May 1984, in an article written by Dewdney in Scientific American (Computer Recreations)."
Info about at: corewars (including links to tutorials/guides, math of the game and even the use of genetic algorithms to evolve core war programs).