I would assume this is a G-line (global ban) from the Undernet IRC network. 'Using exploits' it a little ambiguous, but did you use the mIRC DCC exploit against anyone else? If so, that might be why.
We can't do anything about G-lines, they have nothing to do with mIRC - they are set by the network's IRC operators, and only they can unban you. It could be that someone using your ISP was banned, and they kept evading the ban, so they've had to put an entire ban on your ISP - this means innocent people get affected too.
For further information about what to do if you've been G-lined, check out
this thread.
Regards,
