False positives are regularly returned by a range of antivirus products when running or installing mIRC. This is most likely due to the fact that some trojans do manipulate some of mIRC's default files, or "zombies" make use of mIRC to connect to IRC servers. Nevertheless, downloading mIRC from this website is an absolute guarantee that there is no virus or trojan in the installer package, so you can go ahead and install mIRC safely.
Regards,
