One definition of hack -- not the oldest, but arguably the most prevalent in places other than the Internet -- is (OED)

A person whose services may be hired for any kind of work required of him; a common drudge, esp. a literary drudge, who hires himself out to do any and every kind of literary work; hence, a poor writer, a mere scribbler.

In this sense, it is certainly a negative term (cf. http://en.wikipedia.org/wiki/Political_hack).

One definition of hack — not the oldest, but arguably the most prevalent in places other than the Internet — is, from the OED:

A person whose services may be hired for any kind of work required of him; a common drudge, esp. a literary drudge, who hires himself out to do any and every kind of literary work; hence, a poor writer, a mere scribbler.

In this sense, it is certainly a negative term (cf. political hack).