In Internet slang, the term "grey hat" or "gray hat" refers to a computer hacker or computer security expert whose ethical standards fall somewhere between purely altruistic and purely malicious. The term began to be used in the late 1990s, derived from the concepts of "white hat" and "black hat" hackers. When a white hat hacker discovers a vulnerability, they will exploit it only with permission and not divulge its existence until it has been fixed, whereas the black hat will illegally exploit it and/or tell others how to do so. The grey hat will neither illegally exploit it, nor tell others how to do so.