Book excerpt: Information is one of the biggest businesses in the world today, even among criminals. People called hackers have been around for decades. They break into computer systems to steal private information. They then use it for their own financial gain. Other people also make their living by hacking. But they do it legally. Professional computer hackers use their skills to keep others from becoming the victims of criminal hackers. Part of the series, They Do That for a Living?, Professional Computer Hackers explores the history of this unusual career, what it takes to join it, and where professional hacking is headed in the future.