Welp, first of all, in this day and age of clueless users and net savy dorks, it is quite easy to appear to be well versed in Hacking. That doesn't mean you should live in fear of any asshole well versed in keyboard-fu.
Some simple questions before we get on to the technical goobity gook. First of all, who is this person that is pestering you? What is there motivation for pestering you? What makes you think he is a hacker? Does he say hacker or H@X0R? The prime step in defending yourself is know thine enemy.
Also it would be really helpful if you let us know as much about your setup as possible. This will help us identitfy any significant flaws or exploit goodness. How do you connect through the Internet? Do you have more then one computer on said connection? Do these computers tie into a router (brand is helpful) or a switch? Is your operating system uptodate? and finally, what steps have you taken to protect yourself online?
"Remember how much fun you had shooting spitwads at the teacher in seventh grade? Imagine applying that kind of attitude to actually fucking with Mitsubishi!"
- Jello Biafra