Crapflooding

Flooding or scrolling on an IRC network is a method of disconnecting users from an IRC server (a form of Denial of Service), exhausting bandwidth which causes network latency ('lag'), or just annoying users. Floods can either be done by scripts (written for a given client) or by external programs.

The history of Internet Relay Chat flooding started as a method of taking over an IRC channel other then the original founders of the channel. The first attacks generally used a modified IRC client or an application to flood a channel or a user. Later they started to be based on bots and scripts. This later moved on to starting IRC based botnets which were capable of DDoS and IRC floods.

...
Wikipedia