I still have no clue why the url works for some ppl and gives 404 to others. Maybe it only works for IRC newbies? :P
Anyway, here's another lamer version of the message:
[ALERT] mIRC6.12 has a bad bug, causing laggy chatting, update your mIRC6.12 with a patch file you can get it from [url deleted] and that will update your mIRC to mIRC6.13, ENJOY
That one is more obvious that its a fake, since its using [deleted]...