If a person would type "| exit" without the quotes, your mIRC would exit. Mind that this is even quite an innocent command, one could easily format your hard drive...

Just for accuracy, it wouldn't exit if you typed | exit, but if you are a little smart you will easily know where exactly you need to place the | exit, though I don't want to give too many hints.

Just know that the given code was a real threat to anybody's system who loads that remote in that state.