look at linux which is open source and there is less problems.
You mean 'fewer' problems? While I am at it, your grammar is not the only thing that requires attention. Linux = fewer problems because Linux has a smaller following. If you were the author of a virus, EG: a DDoS trojan, are you going to want to infect 5% of the computers in the world or 90%? Hackers and virus authors arn't stupid, they just lack respect for the privacy of others. They do have an idea of what efficiency and productivity is like and aiming to infect 90% of computers is going to provide a bigger 'bang' on D Day.
If mIRC went open source I would stop using it.