I just wanted to jump in here as well. Hello, and welcome to mIRC!
As far as the script you may have edited, if you downloaded mIRC from here and didn't download any other scripts, what you would have edited is mIRC's own default scripts. They are not necessary for mIRC to run, but they offer a few useful things. Any editing you might have *accidentally* done isn't going to make those scripts dangerous. If anything, you'll prevent something from working correctly. The script(s) *will* still run, but may have an error in one or more parts. Your best option is to just reinstall mIRC and overwrite the files when asked, then you will have the normal version without any possible errors. Basically, you would have to know what you're doing to make a safe script dangerous unless you were extremely "lucky."
As far as scripts and hacking goes, think of it this way... anyone with knowledge can write a "dangerous" script that can be used to do a lot of different things. You should never run a script from someone you don't trust or type something someone tells you to type if you don't trust them. Either thing could cause you problems. That said, there are a lot of very useful (and safe) scripts out there. If you don't want the additional functions, features, changes, games, etc. that those scripts offer, then just don't ever install any scripts and you won't have to worry about whether or not they are safe. However, if you do like those additions, you can go to a scripting site that is trusted and who examine all scripts they have up for download so that you can be fairly positive they are safe to use. Using scripts really isn't any more dangerous than just connecting to the Internet provided you are smart about what you do with them.
And, as mentioned, there are many other ways you could have problems than just through scripts (with and without mIRC). It really all comes down to being smart about what you do whether it's with mIRC or some other online program. Downloading or installing unknown software/scripts can be dangerous, for example. That is true in mIRC and in a browser like Internet Explorer and in FTP programs and any other software that can download files. If you know how to protect yourself, you can usually get away with trying most unknown software without much concern, but if you're not that familiar with protecting your computer, you're better off just avoiding any unknown downloads.
