Have you tried trojan scanners instead of virus scanners? They work in slightly different ways I believe. Personally, I recommend SwatIT
and The Cleaner
You might try seeking help online from one of the many virus helpers that exist on IRC. There's #NoHack
on DALnet, or #VH
on Undernet to name just two. You might try typing, for now, /!remote off
It's registering mIRC with the username 'owned'? That is odd. Just so you know incase you didn't, 'owned' is a word used by stupid people to say that they've been "beaten" or "hacked" etc.. I've never heard of viruses/trojans registering mIRC.
You may also want to check out that thread linked to above and download a firewall. It might help in the future in keeping "hackers" out of your system. That could even be what is happening now, someone may just be continually exploiting your system on an open port. Make sure you have all windows updates from the Windows Update
G'luck with your problem