A botnet refers to a type of bot running on an IRC network that has been created with a trojan. When an infected computer is on the Internet the bot can then start up an IRC client and connect to an IRC server. The Trojan will also have been coded to make the bot join a certain chat room once it has connected. Multiple bots can then join in one channels and the person who has made them can now spam IRC chat rooms, launch huge numbers of Denial of Service attacks against the IRC servers causing them to go down.