IRC takeover war
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Takeover wars have plagued IRC networks for a long time. Due to a design flaw in the original protocol specs, if two servers lost the connection between each other, the channel operators on both sides of the split should retain their status. When one of the servers has no users in a channel during a split, the channel does not exist. People could create that channel by joining it and gain channel operator status. When the servers merged, they could kick out the original operators. This caused problems beyond loss of channels, since attackers would use various (often very bandwidth-intensive) methods to deliberately cause server splits which they would then abuse.
As time has passed, various measures have been implemented to prevent takeovers in different kinds of IRC server software.
The simplest way to prevent this from happening, known as TS (TimeStamp) and implemented in many IRC2 IRCds (such as: Bahamut, DreamForge and others), is to check which channel is newer when two merging servers each have a channel with the same name. If they were both created at the same time, they were the same channel, and operators on both sides should be kept. If one channel is newer than the other, this channel was created later, possibly as a takeover attempt. In this case, the special status of any users in the newer channel is removed when merging.
Many servers have implemented Services or automated bots with special status, to protect channel operators.
Channel creation during netsplits is not the only kind of takeover attempt, however. Other methods include cracking the computers of channel operators or stealing their Services password.
Another popular form of takeover abused a protection system where a user on one side of a netsplit would take the nickname of a target on the other side. When the network reconnected, the servers would "collide" the nicknames, knocking both off the network. The attacker would typically have a second client which would quickly change its name while the original user was reconnecting.
There are two popular methods of stopping nickname collisions - TS (similar to Channel TS, see above) and nickhold. TS involves checking when the nickname was made use of on each server. The connected user that had the nickname first would remain on the server, while the one who took use of the nickname at a later timestamp would be knocked off of the other server via "Nickname Collision." This method is used in many IRC2 IRCds such as Bahamut, Unreal and Hybrid.
The other method is known as nickhold and involves disallowing the use of recently split nicknames. It is known to cause less kills (naturally through the way it works) but causes more inconvenience to users. For this reason, the TS protocol is generally more common.