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Famous as the co-founder of Apple, Stephen "Woz" Wozniak is a little different from other profiles here -- and began a 'white hat' hacking career with 'phone phreaking' -- in other words, ways to bypass a the phone system.
As a student at the University of California, Wozniak made 'blue box' devices for his friends so they could make free long-distance phone calls -- reportedly, one of these items was also used to call the Pope while pretending to be Henry Kissinger.
He later left university to begin working on computer designs, forming the Apple computing system with Steve Jobs. Wozniak designed the hardware and the majority of the software for the first Apple prototypes. Wozniak and Jobs sold the first one hundred of the Apple I to a local dealer for $666.66 each.