If you would like to learn about security that's one thing. Hacking is...
If you would like to learn about security that's one thing. Hacking is another, and if you going the illegal route that is cracking, which is just evil! lol.
But If you truely want to learn about secuity and how to "Hack" (better be protecting from hacks). Then try out setting up your own sever on your network and leave it a little open then try to attack it, then work on the bigger fish, but not ones you don't own.
This is what I do, I do it for fun and to lean how to protect myself and be better in the future of my job after I graduate college