Black hat refers to a person who participates in the act of computer hacking for nefarious reasons. A black hat hacker usually gains illegal access to and exploits computer systems solely for personal gain or satisfaction. Red hat hackers, on the other hand, are usually employed by a company to test the security of their own systems in order to identify security problems that could allow a black hat hacker to exploit them.
Black hat hackers are known for breaking into networks for the purpose of destroying data, leaking sensitive information, or stealing identities and financial information. Sometimes they simply decide to gain access to a website and deface it for no reason at all. A favorite tactic of black hat hackers is to, by breaking into a computer system, acquire sensitive and valuable information, and in-turn, threaten to make the information public if the business fails to pay a specified amount of money.
This type of hacker is often portrayed in popular culture as the stereotypical “bad guy hacker.”