Bots (short for robots) were intended to be macro-like small program that are created for repetitive tasks without human supervision. In MMOGs, because many objectives are reusable and thus mundane, they can become tedious. Many MMOG addicts may spend more than 15 hours a day on the game, and hence could progress at much faster speed than another person who can only spare one hour a day to play. The necessary evil of spending time to “kill monsters” (or other objectives, such as mining gems, or fishing, or collecting items) in order to earn enough experience points (xp) to level up is often referred to as “grinding.” Some MMOG requires users to “level grind” up to level 20 before allowing them to participate in more interesting quest (e.g. Guild Wars). (The term, “grinding,” came from the real world usage, where a tool is repetitively subjected to a grinding stone to be sharpened, as well as the idiom, putting your nose to the grind.) Grinding can be so tedious and repetitive it is often not fun to play. Hence, bots were invented to relieve human of the mundane undertaking.

Players who employ bots would installed the program and let the bot control the avatar to perform the mundane tasks to level grind up to higher levels before taking over. In many cases, bots were employed to mine gems or gold, as in World of Warcraft, and the human players then turn around and see the in-game gold for real world cash. These kind of players (they are not playing at all, but only participate in the game world to perform a task) are known as gold-farmers. Transactions of gold to cash often take place at black market exchange. Second Life is the only game where the trading of its Linden dollar with real world monies, is officially sanctioned. Most other MMOGs do not approve of such transaction because it upsets their game economics.

Here’s an excerpt from Wikipedia on “botting” and it’s effect on Lineage II:

Like many MMORPGs, Lineage II has been the target of botting, in which an external program is used to simulate the actions of a player. Such activity is prohibited and is a bannable offense, though seemingly rarely enforced. Nevertheless, players continue this practice, since the player is able to leave his/her computer and the bot will continue doing what it has been programmed to do. Some of the most well-known bots are L2Walker and Superman (formerly known as L2Wind). There is a conspiracy theory, based on fine coding, numerous features and versatility of those programs (surpassing the official game client by far), that developers of Wind and Walker were/are in league with NC Soft itself. Sometimes proven botted characters are subject to disrespect and rejection by the certain part of the community. But this tendency got terribly weakened lately, legit players having definitely become a minority. Apart from easing some of the more mundane aspects of gameplay, botting can also be used as a way to generate Adena (Lineage II currency) which is then sold for real world cash.

This phenomenon, Economy Interaction, is quite controversial and is common in most of today’s large MMORPGs.