I was looking at the options table in a WordPress install and noticed an option name hack_file. At first I thought the site was compromised and then realized it is a default option http://codex.wordpress.org/Option_Reference . I couldn't find much information regarding it. What is it and its purpose?
As the codex says, it is legacy with probably no use in any modern version. I have been around wordpress since 2.0.4 and I don't remember it being used or referenced so my guess is that it is a really old legacy thing.