The Undernet is one of the largest Internet Relay Chat (IRC) networks.
As of 2007, Undernet is the second-largest publicly-monitored IRC network, with about 20 client servers serving 120,000 users at any given time.
IRC clients can connect to Undernet via the global round robin irc.undernet.org, the region-specific round robins us.undernet.org and eu.undernet.org, or a specific server from the Undernet server list
Undernet was established in October 1992 by Danny "WildThang" Mitchell, Donald "WHIZZARD" Lambert, and Laurent "_dl" Demally as an experimental network running a modified version of the EFnet irc2.7 IRC server software, created in an attempt to make it less bandwidth consumptive and less chaotic, as netsplits and takeovers were starting to plague EFnet. The Undernet IRC daemon became known as "ircu".
Undernet was formed at a time when many small IRC networks were being started and subsequently disappearing; however, it managed to grow into one of the largest and oldest IRC networks despite some initial in-fighting and setbacks.
It is notable as being the first network to utilize timestamping, originally made by Carlo "Run" Wood, in the IRC server protocol as a means to curb abuse.
For a period in 1994, Undernet was wracked by an ongoing series of flame wars. Again in 2001, it was threatened by automated heavy spamming of its users for potential commercial gain. Undernet survived these periods relatively intact and its popularity continues to the present day.
As Undernet limits channel registration to "established channels," or channels with an active userbase, Undernet introduced a version of ChanFix (under nickname C) designed to work like EFNet's ChanFix, its use is to protect unregistered channels. ChanFix tracks channel op usage and restores ops if channels become opless or are taken over.
Undernet also runs an open proxy scanner. This proxyscanner scans users currently connecting to the network for open WinGate, SOCKS version 4/5, and [proxy] servers. IP addresses hosting open proxy servers are automatically G-lined from the network. These changes were put in place after the 2001 Denial-of-service attacks almost destroyed the network and left Undernet without the registered channel service bot for months.