1) Ensure that your anti-virus definitions are completely up-to-date (even if the auto-updater (if your program has one), says they are, manually run the update)
2) If this doesn't resolve the problem, write to the company that issued your software and tell them that their anti-virus software is issuing false positives for IRC and mIRC
3) Check for an option to add an exclusion in your anti-virus program. There should be something, although exactly where and what it's named varies from program to program, and, sometimes, even version to version of the same program.
3a) If you can find this, add IRC and mIRC to the exclusion category.
