The report of mIRC Script Trojan is actually a cautionary message, rather than a true trojan notification. The anti-virus is detecting that mIRC has the capability of being scripted with a trojan virus, however, I'd say probably 99% (or more) of mIRC's scripting capabilities have nothing to do with trojans, and there are several safeguards in mIRC, either on by default or accessible by using a single parameter in a code, to prevent or eliminate this possibility.
If you don't have any scripts, then you are safe. If you do have scripts, then ensure that you know who/where you got the script from, and what each portion of the script does.
If you don't know that, then don't use the script until someone that you do know has had a chance to look at and review the code.
Some of the helpers on this site will be more than happy to review a code if given the location where the code was downloaded from, or if that's not possible, accessing it from one of many pastebins that are available.
