That's true, on both accounts. Hacking is when you get unauthorised access to someone else's system.
Of which can be used to find security holes in companies network's and some people make a living out of doing so and then reporting it to the company in question. It's called white hat hacking.
I personally have an in depth understanding of a variety of DoS attacks and know about encryption. But I've never done any hacking, too bust posting ponies.