HACKERS / CRACKERS
Hacker is a person who is proficient with computers and programming to an elite level where they know most of the ins and outs of a system. They are intensely interested in the arcane and complex workings of any computer operating systems and programming languages, and most often are good programmers. They might discover holes within systems and the reasons for such holes. They constantly seek further knowledge, freely share what they have discovered and never intentionally damage data. In general, there is no illegality involved with being a hacker. Computer programmers insist that the word ‘hacker’ applies only to law-abiding enthusiasts who help create programs and applications or improve computer security.

HACKERS
According to Hackers’ dictionary, Hacker is a person who enjoys exploring the details of programmable systems and how to stretch their capabilities, as opposed to most users, who prefer to learn only the minimum necessary. The one who programs enthusiastically or who enjoys programming rather than just theorizing about programming, capable of appreciating hack value and good at programming quickly. One who enjoys the intellectual challenge of creatively overcoming or circumventing limitations. One might be an astronomy hacker, i.e an expert or enthusiast of any kind. Someone would argue that the people that are now considered hackers are not hackers, as before the media described the person who breaks into computers as a hacker.

Although hacking into network computer systems is illegal, hackers believe it is ethically acceptable as long as a hacker does not commit theft, vandalism or breach any confidentiality — the so-called “hacker code of ethics”. Many hackers believe that it is their responsibility to seek out security holes in computer networks so that systems administrators may fix them. What the hacker does with their knowledge of systems within the definition of the law is what defines them as a hacker vis a vis cracker. It's then safe to say that all crackers are hackers, but not all hackers are crackers. But not all hackers follow a code of ethics. Those who break into computer systems with malicious intent are known in the hacking world as crackers.

CRACKER
Cracker is a person who violates system security with malicious intent. Someone who accesses a computer or network illegally but has the intent of destroying data, stealing information, or other malicious actions. On the other hand the Hacker is a person who used his or her advanced computer skills to attack computers, but not with malicious intent. Cracking is the act of breaking into a computer system, often on a network. A cracker can be doing this for profit, maliciously, or for some specific purpose. Crackers tend to be young and unskilled.

So we can say that a cracker is the one who breaks into or otherwise violates the system integrity of remote machines with malicious intent. Having gained unauthorized access, crackers destroy vital data, deny legitimate users service, or cause problems for their targets. Crackers can easily be identified because their actions are malicious and also known as “Black Hats”.

ETHICAL HACKER
[They can be named as network security auditors]
A computer and network expert who attacks a security system on behalf of its owners, seeking vulnerabilities that a malicious hacker could exploit. To test a security system, ethical hackers use the same methods as their less principled counterparts, but report problems instead of taking advantage of them. Ethical hacking is also known as penetration testing, intrusion testing and red teaming. An ethical hacker is sometimes called a white hat. In the 1970s, groups of experts called red teams to hack own computer systems as initial ethical hackers at US government and now many large companies, maintain employee teams of ethical hackers. Let us now have a look on the categories of hackers;
HACKER CATEGORIES

* WHITE HAT (or Ethical Hackers)
White hat hackers, also known as ethical hackers, or white knights, are computer security experts, who specialize in penetration testing, and other testing methodologies, to ensure that a company's information systems are secure. Such people are employed by companies where these professionals are sometimes called ‘sneakers.’ These security experts may utilize a variety of methods to carry out their tests, including social engineering tactics, use of hacking tools, and attempts to evade security to gain entry into secured areas.

* GREY HAT
A grey hat, in the hacking community, refers to a skilled hacker who sometimes acts illegally, sometimes in good will, and sometimes not. They are a hybrid between white and black hat hackers. They usually do not hack for personal gain or have malicious intentions, but may or may not occasionally commit crimes during the course of their technological exploits. For example, a grey hat hacker may penetrate a computer system without authorization or perform an illegal act. However, the hacker may simply patch the security hole that allowed them access without damaging the system. In this situation, they may or may not disclose their activities, due to legal ramifications.

* BLACK HAT ( OR CRACKERS)
A black hat hacker, sometimes called "cracker", is someone who breaks computer security without authorization or uses technology (usually a computer, phone system or network) for vandalism, credit card fraud, identity theft, piracy, or other types of illegal activity. A black hat is the villain or bad guy, especially in a western movie in which such a character would wear a black hat in contrast to the hero's white hat. The phrase is often used figuratively, especially in computing slang, where it refers to a hacker who breaks into networks or computers, or creates computer viruses.
They are specialize in unauthorized penetration. They may use computers to attack systems for profit, for fun, or for political motivations or as a part of a social cause. Such penetration often involves modification and/or erasing of data, and is done without authorization and hence they should not be confused with “ethical hackers”.

They are a cause for distribution of computer viruses, Internet worms, and deliver spam through the use of botnets. The term may also refer to hackers who crack software to remove copy restriction methods: copy serial number, code and breaking / bypassing legal rights.

* SCRIPT KIDDIE
In hacker culture, a script kiddie, or skiddie, occasionally script bunny, skid, script kitty, or similar, is a derogatory term used to describe those who use scripts or programs developed by others to attack computer systems and networks. It is generally assumed that script kiddies are youth who lack the ability to write sophisticated hacking programs or exploits on their own, and that their objective is to try to impress their friends or gain credit in computer-enthusiast communities.

* HACKTIVIST
A hacktivist is a hacker who utilizes technology to announce a social, ideological, religious, or political message. In general, most hacktivism involves website defacement or denial-of-service [DoS] attacks. In more extreme cases, hacktivism is used as tool for Cyber-terrorism. Hacktivists are also known as Neo Hackers.