Black-hat

A malicious hacker. Refers to color-coded hats in old western movies: bad guys wear black and good guys wear white. More formally, the term is used to refer specifically to malicious hackers who really know what they're doing, but it is also often informally used just to refer to "bad guys" in general.

Contrast and compare white-hat, script kiddie. These are not FreeBSD-specific terms, but they're included here because the terms are relevant to any security discussion.