Virus scanners that are set up to detect scripts and unknown viruses can very easily pick up a "virus" in a mIRC script. I wrote a simple script to backup data on a regular basis and send it to another person so the data couldn't be lost. McAfee called it a virus and deleted it on me until I reconfigured McAfee. That just means the virus scanner is being careful, not that you really have a virus or trojan.
Of course, it is possible you picked up a trojan somewhere. But as far as it being part of Invision... it's not.
Run your virus scanner and find out what *file* is affected by the trojan and post that filename here. We'll be able to tell you if it's part of Invision or not.