You all identified the problem.
I called F-Secure tech support, talked to a man who as usual knows his business, and we:

1. Unloaded F-Secure.
mIRC ran.
2. Loaded F-Secure.
mIRC would not run.
3. Ran F-Secure main screen.
Went to Internet shield.
F-Secure indicated mIRC was malware.
Choices: Delete, Quarantine, Remove from Scan, and ignore.
Chose to remove from scan.
Success!!!!!!!!!!!!!!

Thanks a lot, my friends...

C Barlow