What is ethical hacking and what are the different classes of hackers?

Ethical Hacking: An ethical hacker, also referred to as a 'white hat hacker', is an information security expert who systematically attempts to penetrate a computer system, network, application or other computing resource on behalf of its owners and with their permission to find security vulnerabilities that a malicious hacker could potentially exploit. Hacking Computer System: Hacktivism attacks those including Famous Twitter, blogging platform by unauthorized access/control over the computer. Due to the hacking activity there will be loss of data as well as cause damage to the computer. Also research indicates that those attacks were not mainly intended for financial gain too and to diminish the reputation of particular person or company. A hacker is an unauthorized user who attempts to or gains access to an information system. Hacking is a crime even if there is no visible damage to the system, since it is an invasion in to the privacy of the data. There are different classes of Hackers. White Hat Hackers - They believe that information sharing is good, and that it is their duty to share their expertise by facilitating access to information. However there are some white hat hackers who are just "joy riding" on computer systems. Black Hat Hackers -They cause damage after intrusion. They may steal or modify data or insert viruses or worms which damage the system. They are also called 'crackers'. Grey Hat Hackers - Typically ethical but occasionally violates hacker ethics. Such hackers hack into networks, stand-alone computers and software. Network hackers try to gain unauthorized access to private computer networks just for challenge, curiosity, and distribution of information. Crackers perform unauthorized intrusion with damage like stealing or changing of information or inserting malware (viruses or worms).