A black hat (black hat hacker or blackhat or threat actor) is a computer hacker, who disobeys laws or violates ethical standards for purposes such as civil disobedience, cybercrime, cyberwarfare, or malice. These acts can range from piracy to identity theft. A black hat is often referred to as a "cracker". It is worth noting that the term "Black Hat" is also used outside of direct infrastructure hacking; in digital marketing, "Black Hat SEO" refers to practices that violate search engine guidelines to manipulate rankings, which is distinct from malicious cyber warfare or cybercrime. It is important to observe that the phrase “Black Hat” can also be applied in a context other than cyber attacks against the infrastructure. In marketing, for example, “Black Hat SEO” describes a technique involving manipulation of search engine ranking through tactics that contravene search engine policies.

The term originates from 1950s westerns, with "bad guys" (criminals) typically depicted as having worn black hats and "good guys" (heroes) wearing white ones. In the same way, black hat hacking is contrasted with the more law-abiding white hat approach to hacking. Additionally, there exists a third category, called grey hat hacking, characterized by individuals who hack, usually with good intentions but by illegal means.