If it returns exactly when you start mIRC, then there is likely a script loaded into your mIRC that is creating the virus file.
Start your mIRC, then type:
/remote off
Close mIRC, then delete the virus file. Start your mIRC again and see if the virus file comes back. If it doesn't come back, then you have a bad script loaded into your mIRC. Unload any unknown scripts.
If the virus file DOES come back after you typed /remote off, then there is a separate program running that is creating the virus file, not mIRC. Use an antivirus scanner in safemode to get rid of that program.
-genius_at_work