I am sorry that your server/clients are being affected. However, the protection is easy, and I gave two bits of advice above that, if followed, will protect you.
I'm afraid your servers are not representative of the whole of IRC, and the fact that it is an issue on your servers does not mean it is "widespread".
when someone first installs mIRC, the 'auto-join channel on invite' is automatically enabled.
No it isn't.
Regards,
