Still sounds like you're infected, mIRC does not run itself, nor does it run in the background after you've closed it.
Scan with more than one virus scanner, no ONE detects all variants of all viruses.
If you're sure you're not infected, it's got nothing to do with mIRC, it's the poor method of the IRC network to detect infected drones, so contact the network that you're getting banned from.
Regards,
