there is some command someone can use and if you have an older version of irc, the command will crash your client. It is a major bummer if your grabbing a big file and someone decides to stop it.mIRC 6.12 has been released! (October 13th 2003)
mIRC v6.12 has been released to address a remote vulnerability found yesterday, capable of crashing your mIRC. The vulnerability affects versions of mIRC from v6.0 onwards, so it is highly recommended that you upgrade to mIRC v6.12. You can do so by downloading the new mIRC from the download page!
go here to update: http://mirc.com/get.html