Computer Security/Who is a hacker?

Who is a Hacker?
A Hacker is someone who has exceptional knowledge in Computer Hardware as well as Software and one who uses his or her knowledge wisely to break into other systems. It may be for the purpose of stealing or modifying information, which is unlawful and unethical, or to test the vulnerabilities of a system which helps to develop security tools to protect the system. The term "Crackers" generally means using softwares to get the password and username of someone else account. They are also known as Black Hats.

There is nothing wrong in saying that Linux is a contribution of Hackers, sometimes called Red Hat Hackers, or "Red Hats" -from "Red Hat Linux", a well-known commercial distribution.

True Hackers want to share their knowledge with others and receive knowledge from others as well.

At the same time, however, there are hackers who will break into servers as described above, but not for malicious reasons, White Hats who break into systems to find and alert administrators or fix the system themselves. Sneakers and Tiger Teams would come into this category. As well as these, there are Grey Hats who will break into systems for the greater good, such as illegally breaking into a company's network to find information related to embezzlement.

Hackers attack and disrupt adversaries for various reasons.
 * Advanced persistent threat
 * Most likely a national government
 * Cyberterrorism
 * Hacktivism
 * i.e. [Wikipedia: Anonymous(group)]]
 * Script kiddie