The detection name Backdoor:W32/IRCBot is used to identify a member of a large group of programs that install a backdoor on an infected machine.
The backdoor will then log onto Internet Relay Chat (IRC), the popular instant messaging (IM) system. It may then act as an IRCBot, a type of "bot" that an attacker can control from a modified IRC client.
IRCBots can be used for a variety of malicious actions, such as controlling backdoors or botnets. Backdoors allow a remote attacker to control an infected machine, while botnets can be used to harness a the collective resources of infected machines to perform more resource-intensive actions, such as sending out massive quantities of spam or launching major Denial of Service (DoS) attacks.