No, they don't know. That's why there are a number of $decode infections going around IRC. There have been for years.
However, it has nothing to do with mIRC, it has to do with the intelligence of the end user - I was a newbie once too, and I have never written a $decode virus or anything else other people have asked me to type.
People should not be on IRC, or even the Internet, if they don't know basic ways to protect their computers - unfortunately, IRC and again, the Internet, is a fairly unmoderated medium and you don't need a license to connect to either. This means people get on when they don't know what they are doing. This is not mIRC's fault. All we can do is, everywhere possible, communicate to new users basic protection methods that they can use to keep their computers/mIRC clients clean of infection.
We cannot force people to read documentation if they are too lazy to do so. We cannot force people to install antiviruses, and we cannot cure people's temptation to write commands because they think it'll get them ops in some channel. It's not an mIRC bug.
Regards,
