[University of Maryland: from hacker]
1. A person, similar to a hacker, who enjoys exploring the details of programmable systems and how to stretch their capabilities. Whereas a hacker tends to produce great hacks, a whacker only ends up whacking the system or program in question. Whackers are often quite egotistical and eager to claim wizard status, regardless of the views of their peers.
2. A person who is good at programming quickly, though rather poorly and ineptly.