Hacker

A hacker is someone who possesses an unusually high skill in the arts of computer science and programming, and uses these skills to infiltrate computer systems, networks, and other secure platforms.

Legality
Hacking, while officially considered a criminal act (social terrorism), is not always malicious or harmful. Government agencies and large corporations may hire former hackers to help them protect their networks, intranets, and security systems. Inversely, these same organizations may employ them to hack into these areas of other organizations.

The government agencies who hire former hackers usually do so in return for the exoneration of the hackers' past crimes.

Applications
Hackers are also responsible for software cracking (removal of security features), the creation of malware (adware, viruses, trojans, etc.), and the maintenance of malware databases.

Criminal Minds
A/V tech Penelope Garcia is officially labeled by the FBI as the world's most dangerous hacker. Her skills have served the BAU well in almost every episode. She was hired in return for exoneration of her previous illegal activities.

Real World Hackers

 * Steven Levy, the first official hacker and "coiner" of the phrase
 * Bill Gates is sometimes referred to as a hacker, as his original operating system was based on code written by Xerox in the early 80s.