Your Adf.ly link is
http://adf.ly/QxRt3
The unauthorized mirror is a RU site for the thread (That means you can't use DMCA on anything hosted on the site but the thread is free advertising). The download link for the Adf.ly link is
http://adf.ly/QxRt3 (Same as your link so fine for revenue). The thread does not credit you directly but links to your hosting page. The site has a direct link to the file (Causes loss of revenue). DMCA sadly does not apply outside of the first world so their is nothing you can do about the download link.
Except for the fact that this thread links directly to the file it is good advertising for your mod.
To solve the issue with this direct link in this you have a few options.
A) Take the ~800 direct downloads since 6-23-2013 as a loss.
B) Ask the thread author to remove the direct link.
C) Ask the site to remove the direct link.
D) Announce to your many users (~16,100 by the planet minecraft page) that you are having problems with bootleggers.
E) Do option D and announce that the next version will be delayed because of problems with bootleggers. (WILL reduce your fan base!!!)
All of these options have advantages and disadvantages. I would do option A or option D if it was my mod because it is the most hassle free options.
If you want to get more info before you make your decision you should change you download link to be from "Adf.ly > File" to "Adf.ly > Goo.gl > file". This would add Goo.gl to the chain and give you demographics about how your link is used. It will also add protection form directly linking to the file because they will link to the Goo.gl and you will be-able to see the source for the direct link in goo.gl info. Be sure to have adf.ly first in the chain and no other advertising page in the chain to stay within the adf.ly EULA)
If you do a Goo.gl post the info link here so we can help analyze the data (EX: The info link for "goo.gl/test" is "goo.gl/info/test")
EDIT: After taking forever to write this post and seeing the damage I would recommend option D and you to add the goo.gl to your link chain.