actually in all honesty, it's very very easy to get someone's personal information online, without even doing anything even vaguely illegal.
HOWEVER, what this guy was doing IS illegal.
if he gets it from any other source than your machine, basically, unless he accesses THOSE machines in an illegal fashion, it's legal - but getting the information from YOUR machine is not just sorta but jail-time type illegal.
sadly, there are literally hundreds of programs that can allow a malevolent computer user to view private data on your computer, as well as do lovely things like open / close you cd drives, cause unauthorized accesses to your hard disks, change your desktop, and give you the infamous Blue Screen Of Death.
there are ways around this.
ZoneAlarm, as mentioned earlier, is free, and pretty good; the only disadvantage it really has is that it doesn't bother to tell you what IT's doing, so if you, like me, are wary of letting anything you don't completely understand run on your machine, it's not so good.
i personally use BlackICE defender Pro; it not only blocks access attempts from the outside to my computer, but also logs the IP addresses and whois lookup info for anyone who tries to access my machine - kind of like caller ID for computers.
which, of course, let's you report them to their ISP much more easily.
if you want to learn a whole lot more about computer security, and you don't mind consorting with questionable people, Astalavista Security Group is a crew of (relatively) white-hat hackers that try to keep people informed of security vulnerabilities in their operating systems, and how to prevent hacker access; it's a good site to read up on.
also, as a post-script, now that i think of it, if you talk to a guy in yahoo messenger or icq and he's giving you hell, open a command prompt (Start -> Programs -> Accessories -> MSDOS prompt or "command prompt" depending on your OS version) and type netstat -n to get a list of all open IP addresses - this will list EVERY computer that is currently connected to yours. write down the individual strings of numbers - usually in the following format: "10.10.45.2:80"
next, type ipconfig -all to see a list of way more stuff about your internet connection than you need to know.
the numbers there that you're interested in are the ones for your DHCP server, and your DNS servers, and if your computer is using WINS that server too.
no, you don't need to know what they mean, just look for the labels.
compare the numbers there with the ones in the list from netstat, and cross off any duplicates.
what's left, should be the IP address of your harasser.
then go to Network Tools and put the IP address (just the 10.10.45.2, not the :80 part) in the box right above the Submit button, then click Submit.
Give it a second to run.
this will give you his computer's identifier, then you can go look it up with his ISP
now, when he sez "your home address is:"
you can say "yeah, well yours is:" and give him a link to mapquest image of his house. ( Mapquest is here.)
Go Get 'Em.
[This message has been edited by NapalmsConstantlyConfused (03-20-2002 01:37 AM).]