Is it possible for someone to make you quit irc then take on your nick. I have used the same name for years on undernet then just in the past week or so someone has been on using the same nick as mine. Tonight i was on as my original nick (the one i have used all the time) but then I quit all of a sudden and when i went back on, just in a matter of seconds, my nick had been taken again. If someone can do that is there any way of stopping it?

Sorry just realised this is the message i got when i quit

* You were killed by Ede.NL.EU.UnderNet.Org (*.undernet.org (older nick overruled))
-
Closing Link: FallGuy by Ede.NL.EU.UnderNet.Org (Killed (*.undernet.org (older nick overruled)))

What does this mean?

Well actually it`s a common thing on undernet for people to flood someone untill they crash his mirc, and then to stole their nick just for fun or because they like the nick too much.

However in your case it`s another story. There are 25 servers on undernet. Before you joined irc that day, someone used the nick before you but it went into split. When you logged you used the nick, but when the server that splitted came back, your server killed you, because the one using your nick signed in before you did.

Hope you`ll understand...if not, someone will explain it better.

That's pretty much one of the best explanations I can think of.

Hm... say there is "server1.undernet.org" and "server2.undernet.org"
this servers toogerther are undernet network.
Note: When there is a split it means that something went wrong in connection of server1.* and server2.* so the users that are in server1 cannot see users in server2.* and the same for users in server2.*

At the moment are toogether

at 9:00 in the morning there was someone in the server2.* with nickname FallGuy (for example ). Users from server1.* could see him and talk to him because the servers were toogether.

at 10:00 in the morning a net split occured and server2.* splited with server1.* now users in server1.* saw user FallGuy quitting with reason (Net*Split) but actualy he didn't quit he is just in server2.* and can no longer see him users from server1.*

at 11:00 you join server1.* with nickname FallGuy. Everything ok because there is no nickname FallGuy in the network (at the moment the network is only server1.*)

at 12:00 server2.* comes back with server1.* but something is wrong here. There are 2 users with nickname FallGuy. So the user who came last (and in this case its you) gets quit with the message you saw and the other continues regulary in UnderNet.

I hope if you didn't understand with andrews' desc you understand better with this one

Netsplits are (unfortunately) a routine part of IRC life. What the above message means that NickName, who you were on a channel with, was on a different server from you. This server split off from the part of the net you were on.
Note that netsplits are all from a point of view of the user. After a netsplit rejoins people might say to you "where did you go?" -- because from their perspective, *you* split off.

The only thing you can do during a netsplit is wait for the net to mend itself. Changing your server during a netsplit is a Bad Idea, because you are likely to get nickname collided. By changing servers, you may also be contributing to the lag.

As long as you don't quit your client, any DCC chat or send will still work, even during a netsplit (unless the netsplit is because of a specific rare hardware problem).