People can only get into someone else's computer if it's insecure in some way, which granted a considerable amount are. But even then there are very few that would be described as 'easy' to get into.
Anyway, zfr is only showing how to make mIRC show the IP/hostname of a user, something which mIRC already is given by the server but doesn't always display. Every time you go on IRC people can get your IP (or the IP of a bouncer you went through to get onto IRC), unless there's a usermode specifically there to hide it (often +x). While hiding your IP from people on IRC can give you a slight amount of added security, it's really pretty unlikely that anyone would happen to be on an IRC network of thousands and suddenly decide that they want to try and crack you of all people, unless of course you're deliberately antagonizing someone - yet another reason not be a jerk on IRC. Besides, any time you do anything on the net dozens of people get your IP, after all the very act of being online is to be connected to other computers, so you should always take steps to secure your computer with active virus protection, a decent firewall, and checking software vendor's websites for security fixes.
