There is already enough spam around the place anyway, and as I said it would return as "http://infected.site.foo mIRC!" when the option is disabled, otherwise it would show as "mIRC" where you can click it and it will be a normal hyperlink.
When the option is disabled by default that will allow people who are actually understand about IRC spam to enable it, because I believe people who don't know about dangerous spam are the same people who wouldn't know how to tick a checkbox in the mIRC options.
