Kevin Mitnick

The title of “World’s Most Dangerous Hacker” has been much contested. These final two hackers have both been given it at different points but Kevin Mitnick is now a respectable businessman specializing, as so many former hackers do, in improving the security of their clients’ firms. But this reform has come at the end of a 5-year prison sentence, itself stemming from the violation of a previous sentence (Mitnick committed a hack at the end of his supervised release period). He was arrested in 1995 after breaking into the Department of Justice computers and was said to be able to launch nuclear missiles by whistling down a payphone. The claims may have been exaggerated, but it’s easy to see why he was considered the most dangerous man in the world back in the 1990s.