The most common and most likely answer to this crossword clue is the 9 letter word SCRIBBLER
I've seen this crossword clue in Financial Times
S
C
R
I
B
B
L
E
R
Buddy explains!

The straight part
We know that "Hack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hack = scribbler.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SCRIBBLER mean?
SCRIBBLER noun- One who scribbles; a hasty or untalented writer or artist.
- A machine for coarse carding or teasing of wool.
- A ruled notebook or exercise book, especially in grade school.