"Hack" is a word with very broad general meaning. Often it just means to work with a certain type of code, or to find a workaround solution to something. It does NOT always mean, to illegally change the code of a program directly or bypass program security (although that is one meaning).
Source: The Free On-line Dictionary of Computing, © 1993-2004 Denis Howe
hack
[very common] 1. n. Originally, a quick job that produces
what is needed, but not well. 2. n. An incredibly good, and perhaps
very time-consuming, piece of work that produces exactly what is
needed. 3. vt. To bear emotionally or physically. "I can't hack
this heat!" 4. vt. To work on something (typically a program). In
an immediate sense: "What are you doing?" "I'm hacking TECO." In a
general (time-extended) sense: "What do you do around here?" "I
hack TECO." More generally, "I hack `foo'" is roughly equivalent to
"`foo' is my major interest (or project)". "I hack solid-state
physics." See Hacking X for Y. 5. vt. To pull a prank on. See
sense 2 and hacker (sense 5). 6. vi. To interact with a computer
in a playful and exploratory rather than goal-directed way.
"Whatcha up to?" "Oh, just hacking." 7. n. Short for hacker. 8.
See nethack. 9. [MIT] v. To explore the basements, roof ledges,
and steam tunnels of a large, institutional building, to the dismay
of Physical Plant workers and (since this is usually performed at
educational institutions) the Campus Police. This activity has been
found to be eerily similar to playing adventure games such as
Dungeons and Dragons and Zork. See also vadding.