Mitnick was best known for the crime spree during the 1990s that involved the theft of thousands of data files and credit card numbers from computers nationwide. He used his skills to work his way into the nation's phone and cell networks, vandalising government, corporate and university computer systems. Investigators at the time named him the "most wanted" computer hacker in the world.
He scared the pants off the big corporates who found that he had their trade secrets.

In 1995, after a more than two-year-long manhunt, the FBI finally caught him and he was charged with the illegal use of a telephone access device and computer fraud.

While he awaited sentencing, a group of supporters commandeered The New York Times website for several hours, forcing it to shut down.

Mitnick pleaded guilty to computer and wire fraud as part of an agreement with prosecutors and was sentenced to 46 months in prison. He was also prohibited from using a computer or mobile without the permission of his probation officer for the three years following his release.

Mitnick emerged from his final prison term, which he deemed a 'vacation,' in January 2000. He was a changed individual, and began constructing a new career as a White Hat hacker and security consultant. He became a highly sought-after global public speaker, a writer and established the successful Mitnick Security Consulting.

In November 2011, he became the Chief Hacking Officer and part owner of the security awareness training company KnowBe4, founded by close friend and business partner Stu Sjouwerman.