Whilst I was writing that answer I did consider suggesting /!remote off - however, that is only a temporary fix and also disables other possibly useful scripts that they may have.
A lot of the time IRC viruses are activated through scripts and /remote off will help. But as soon as remotes are enabled again, so will the 'virus'. A more permanent removal of the script is needed, and as I can't possibly say exactly what they are infected with, if infected at all, I think a professional and proper scan with well known antiviruses is the best course of action to take
It can't do any harm to run a full virus scan anyway - to have probably contracted this virus it is likely they are not aware of the dangers of IRC or the Internet (i.e. clicking URLs, typing things to get ops etc etc) - so it's possible they may also have a trojan of some description that has not made any visible marks on their system yet. A simple /remote off would obviously not effect this. Often a virus scan can turn up more than expected.
But yeah, if you're scanning with mIRC open (which I do not recommend) then /remote off is a good idea to try and prevent spamming for now.
Regards,
