If i'm not wrong, there is the l2net's source code repository. With this we'll be able to know about its behavior and detect its users.
But.. we are open source too, so this can become an endless war

Anyways, this goes for all the devs here: Kill all these fvcking bots!! Even if it isn't done in l2jserver

I'll begin working on it soon for my part. The problem is that if I publish something, the bot devs will maybe program something against it...
PS: I have just made an svn checkout

PS2: If you want it for the l2j client... C# is very similar to java

PS3: I don't have the visual C# right now, so I didn't compile it to check if it is the real l2net last version... so this post is maybe an epic fail (i warn xD)