All of the above answers are wrong.
ConferenceRoom has it's own dedicated java applet run by it's own dedicated webserver. The IRCd can easily tell if a user is a real +j client or not and indeed tell if it is the CR applet or a third party one. There are also many ways for opers to distinguish between the two.
Now for the tricky bit: It is possible (and I am not going to broadcast how) to set mIRC up to trick CR into thinking that you are running it's java applet simply because IRC is a plain text based protocol and therefore anything is possible if you know how. If you restrict your room to java-only, there will be bound to be some immature git who thinks it is l337 to try and breach it. Regardless of what they try though, an oper will usually be able to tell and opers that has experimented with it, such as me, will be able to tell, regardless. They think that alteration of version reply and the two-three raw commands is enough to 'hide' what they are doing - wrong.
Anyway, in short, CR is able to tell simply because it is a total package. Most networks consisting of IRCd + BOPM + Services + jPilot still don't have the rich feature list of CR and don't have the integration of CR, and probably never will have.
By the way, +j can't be used on it's own. It is a supplimental mode for +k <key here>. You need to set the key first then set +j. You and your hosts can simply use /cs invite to get in rather than having to remember a lengthy key.
