Internet chat software works by connecting to a server on the IRC network. IRC servers connect to each other to create a large networks, one examples being EFNET and IRCnet. Using chat software and chat server software, a user (referred to as a client) connects to the IRC network of his or her choice, and then can choose to join different channels, which function like an online chat room.
An online chat room is named by topic, and propagates throughout the network on chat server software. Originally, IRC functioned almost entirely on the UNIX platform, and many pieces of chat software exist for UNIX and its various flavors. By far the most popular piece of chat software for Windows user is mIRC, which makes using IRC and navigating its networks easier than the command line interface provided by the UNIX system.
Using mIRC, a user can connect to network and join chat rooms through menu functions, rather than entering IRC commands directly. Once a user enters joins online chat room - a channel - a windows will open up in mIRC displaying whatever messages are being typed by other users in the room (who are shown in a separate window on the right.) In this way mIRC chat software makes it easier for the average user to navigate the IRC network.
While originally IRC was used mainly for online chat, it has evolved to become a major source of file distribution. Built into the IRC network are protocols to exchange data (DCC, XDCC) which allow users to send each other data files. With the advent of windows-like IRC chat software, it has become easier for more people to partake in this once complicated process.
Many online chat rooms that operate for the purpose of file exchange are populated with many 'bots' which act as file servers. The bot is a piece of software that functions as another user on the network, so a bot would have a name in the online chat room just as a regular user would. Through a set of commands, often specific to each chat room, the user uses his or her chat software to send a message to the bot, which automatically responds with a list of files served. The user may then request a given file and the bot will send it to him or her, exactly as two real people would exchange files.
It's important to note that the IRC network is not another incarnation of peer-to-peer filesharing: all files are sent directly from one user (usually a bot) to another. There is no wide distribution or bandwidth sharing amongst multiple peers. Nevertheless, partially because of its smaller user base and its relative difficulty, the IRC network has gained a reputation as a major source for the distribution of digital copyrighted material.
Before windows IRC chat software existed (namely mIRC) participation in the network would have been very difficult for the average user, as strong computer knowledge was required. Compared to many p2p networks used today, IRC still remains difficult to use, and for this reason manages to stay more or less below the radar of organizations that target illegal file sharing. It remains to be seen, however, how long this will remain the case, and IRC chat software is constantly improving, and thus becoming easier to use.