If you've ever worked with open-source software such as Linux, Wordpress, Drupal, phpBB, etc., you may have run across the title of this article. Never hack core! But what does that mean? Doesn't the whole premise of open-source involve people tweaking and (hopefully) improving the core code? Yes -- but in a very controlled way that usually involves many eyes on the code verifying that the change is a good one which will benefit the program as a whole.