Sometimes anti-virus or firewall software may incorrectly think that mIRC or the mIRC installer contains a trojan/virus when it does not and will block it from either running or from connecting to the internet. This is called a false-positive and usually happens when the anti-virus or firewall software is not aware of a new version of mIRC. You would need to check your anti-virus or firewall software to make sure that it is updated to the latest signatures and possibly to change their settings to allow the new version of the mIRC installer and/or mIRC to run correctly.
