simple security

Black hat hackers:
Black hat is a skilled hacker who uses his or her ability to pursue their interest illegally. They are often economically motivated, or may be representing a political cause. The term comes from old Western movies where heroes typically wore white or light-colored hats and outfits, and the villains wore black outfits with black hats.

Grey hat hackers:
Grey hat is a skilled hacker who sometimes acts legally and in good will and sometimes not. They are a hybrid between white and black hat hackers. They hack for no personal gain and do not have malicious intentions, but commit crimes.

White hat hackers:
White hat is a hacker who is ethically opposed to the abuse of Computer systems. S/he generally focuses on securing IT Systems

Also, a hacker as described by Wikipedia:
Hacker is a term used to describe different types of computer experts. Currently, "hacker" is used in two main ways, one pejorative and one complimentary: in popular usage and in the media, it generally describes computer intruders or criminals; in the computing community, it describes a particularly brilliant programmer or technical expert (for example: "Linus Torvalds, the creator of Linux, is a genius hacker.").