A hacker, as referred to in the mainstream context, is someone who is able to gain unauthorized access or break into a computer system or network by identifying and exploiting weaknesses in it. To do so, the hacker may do something as easy as crack someone’s password, or as complicated as engineering a computer program to break someone’s computer security software.

A hacker may be motivated by bad intentions (black hat hacker or cracker), good intentions (white hat hacker), or a combination of both good and bad reasons (grey hat hacker).

1)      Black Hat – These hackers are the really bad ones and also the ones known within the industry as “crackers” rather than hackers. They have only malicious objectives behind compromising computer security. They get personal gains through any of various cybercrimes they may commit by hacking including identity theft, theft of credit card numbers, piracy and vandalism. Whenever they discover vulnerabilities, they keep this knowledge to themselves instead of informing the victim organization or entity. If at all they try to fix or patch the loophole, it is purely to maintain their reigning power.

2)      White Hat – These are non-malicious hackers who hack their way through security systems for legal, ethical or good reasons. One example of the work that such a hacker would perform is to try to break into an organization’s systems at the organization’s request so as to test how secure the systems are. This is called penetration testing and is a form of “ethical hacking.” Should the hacker discover a security vulnerability, he would reveal the same to the concerned party so that the needful can be done to fix the vulnerability before a black hat/grey hat hacker actually gets into the systems.

3)      Gray Hat – These hackers display some characteristics each of the black hats and white hats. A gray hat hacker would freely hack a computer or website without permission. This is the illegal part. However, if the hacker identifies a flaw in the security system, he would inform the administrator or information technology team of the flaw, or sometimes make it known publicly. He may offer to correct the glitch or else give the organization time to fix it themselves. That’s the white part of the gray hat hacker’s activity.

A hacker may use any of various tools to achieve his ends. The list includes computer viruses, password cracking, spoofing, Trojan horses, Rootkit and packet sniffer.