To hack means to chop roughly. It is also used to denote the often illegal computer activities of system penetration known as hacking.
A hack is a poor quality alteration in software or hardware engineering, usually done quickly and ignoring standard practices, in order to meet deadlines. Such a hack may, or may not, be considered a bug depending upon its side-effects.
Hack is also a slang term for a low-grade, unprincipled person, often a writer or journalist. This usage is taken from an earlier usage in which a hack was a hired horse. Such animals were normally of poor quality.