look up different telnetds, is it a *nix or windows machine, find out the OS and the default version of the telnet server deamon there running. Then you probably have some testing you need to do on it to figure out what kind of security it has, I think default is after three failed attempts it will close the session. Im not positive about this though. Administrators can set up there security policies how ever they want, for example to refuse connections from an address after and most login attempts are logged. There is some basics to get you started on writing one.