Bots

Generally a bot is a computer program that simulates human conversation, or chat, through artificial intelligence. Typically, a chat bot will communicate with a real person. Chat bots are used in applications such as e-commerce customer service, call centers and Internet gaming. Chat bots used for these purposes are typically limited to conversations regarding a specialized purpose and not for the entire range of human communication.

Now the bots you encounter in the Yahoo Chat Rooms are generally ad bots, they are there to trick/convince you into going to a web site and purchasing there product. The majority are for Web-cams and/or Pornography Sites.

There are also bots that are created to cause trouble, such as booting bots. And some are more useful for chats that allow room hosting as they can manage a chat room and even entertain the guests in your chat room. Read this thread for more information on some bots available for Yahoo! Chat.