Types of Hackers on the basis of activities performed by them.

A Hacker is a person who is interested in the working of any computer Operating system. Most often, Hackers are programmers. Hackers obtain advanced knowledge of operating systems and programming languages. They may know various security holes within systems and the reasons for such holes. Hackers constantly seek further knowledge, share what they have discovered, and they never have intentions about damaging or stealing data.

Who then is a Cracker?

•  A Cracker is a person who breaks into other people systems, with malicious intentions. Crackers gain unauthorized access, destroy important data, stop services provided by the server, or basically cause problems for  their targets. Crackers can easily be identified because their actions are malicious.
• Whatever the case, most people give Hacker a negative outline. Many malicious Hackers are electronic thieves. Just like anyone can become a thief, or a robber, anyone can become a Hacker, regardless of age, gender, or  religion. Technical skills of Hackers vary from one to another. Some Hackers barely know how to surf the Internet, whereas others write software that other Hackers depend upon

White Hat Hacker

• A White Hat Hacker is computer guy who perform Ethical Hacking. These are usually security professionals with knowledge of hacking and the Hacker toolset and who use this knowledge to locate security weaknesses and implement counter measures in the resources.
• They are also known as an Ethical Hacker or a Penetration Tester. They focus on Securing and Protecting IT Systems.

Black Hat Hacker

•  A Black Hat Hacker is computer guy who performs Unethical Hacking. These are the Criminal Hackers or Crackers who use their skills and knowledge for illegal or malicious purposes. They break into or otherwise violate the system integrity of remote machines, with malicious intent.
• These are also known as an Unethical Hacker or a Security Cracker. They focus on Security Cracking and Data stealing.

Grey Hat Hacker

• A Grey Hat Hacker is a Computer guy who sometimes acts legally, sometimes in good will, and sometimes not.
• 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.
• They are hybrid between White Hat and Black Hat Hackers.

Hactivism 

• Another type of Hackers are Hacktivists, who try to broadcast political or social messages through their work. A Hacktivist wants to raise public awareness of an issue. Examples of hacktivism are the Web sites that were defaced with the Jihad messages in the name of Terrorism.

 Cyber Terrorist

• There are Hackers who are called Cyber Terrorists, who attack government computers or public utility infrastructures, such as power stations and air-traffic-control towers. They crash critical systems or steal classified government information. While in a conflict with enemy countries some government start Cyber war via Internet.

Script Kiddies

•  Next and the most dangerous class of Hackers is Script kiddies, They are the new generation of users of computer who take advantage of the Hacker tools and documentation available for free on the Internet but don’t have any  knowledge of what’s going on behind the scenes. They know just enough to cause you headaches but typically are very sloppy in their actions, leaving all sorts of digital fingerprints behind. Even though these guys are the teenage Hackers that you hear about in the news media, they need minimum skills to carry out their attacks.
• Script Kiddies are the bunnies who use script and programs developed by others to attack computer systems and Networks. They get the least respect but are most annoying and dangerous and can cause big problems without actually knowing what they are doing.

Coders

•  The Real Hackers are the Coders, the ones who revise the methods and create tools that are available in the market. Coders can find security holes and weaknesses in software to create their own exploits. These Hackers can use those exploits to develop fully patched and secure systems.
• Coders are the programmers who have the ability to find the unique vulnerability in existing software and to create working exploit codes. These are the individuals with a deep understanding of the OSI Layer Model and TCP/IP Stacks.