I do not understand logic of blocking Digg. Digg is used by a lot of users. After installing this plugin, my users cannot Digg my site any more.
After Google'ing, I came across many links , e.g. http://nancyradlingerjustmyopinion.com/2012/03/bad-behavior-what-is-it-and-how-frustrating-it-can-be.html, frustrated by Bad Behavior to block Digg.
Perhaps you should mention that upfront in "Installation" or "Description" page. It could save users frustration and time. I am deleting this plugin, after wasting 24 hours on trying to troubleshoot, why my visitors cannot any more Digg my site.