The CTCP version command and reply has the following command format and functions.
/ctcp TheNick version
will return client version information about TheNick.
SYSTEM TheNick CTCP: VERSION http://www.mibbit.com ajax IRC Client .2620 SYSTEM AnotherNick CTCP: VERSION mIRC v6.35 Khaled Mardam-Bey SYSTEM YetAnother CTCP: VERSION Eteria IRC Client STSTEM AndAnother CTCP: VERSION Snak for Macintosh 4.13 English SYSTEM ThisOneToo CTCP: VERSION xchat 0.24.1 Linux 2.6.27-8-eeepc i686 SYSTEM SomeLie CTCP: VERSION Mirc SYSTEM FunnyGuy CTCP: VERSION You could at least buy me a drink first.
and other variations, depending on the client.
If TheNick is using a Mibbit Client, the response is always sent.
It needs to be said, that some clients allow this information to be added to, with extra lines, modified in such a way to lie about the version, or even block it from responding at all.