There are numerous addons flying around scripting websites which claim to block the exploit, however, there are several different variations of it so I doubt that any of them block them ALL.
The safest way is to just use
/ignore -dw * - if you're determined to downgrade that is.
As for that DLL, I suggest searching around
www.mircscripts.org (it has a search feature) and also contacting the author of the DLL to let him know that he is meant to work with mIRC, not the other way round
G'luck, and happy chatting.
Regards,