Good news! Update on the situation - check your titles on the site, they may have removed them. (Mine are gone.)

The website ebooks-tree.com has somehow made a lot of fanfic works available for download from their site without author permission. (And they're charging, so adding insult to injury.)

If you have ever published a story (particularly on AO3, as that seems to be where the bulk have been culled from) please go to the ebooks-tree-com site and do a search for the name under which you posted the story.

Here's a link to fyeahcopyright on tumblr, with updated info on what you need to file a DMCA (copyright infringement) complaint. (Don't let ebooks-tree's website scare you, they word it as obscurely as possible so it seems intimidating. fyeahcopyright has done a great job of making it much more clear and straightforward.)

Here's the info on how to submit a DMCA complaint (copied almost verbatim from fyeahcopyright on Tumblr.)

Submit all the info via http://www.ebooks-tree.com/info.php?contacts with DMCA Complaint in the subject

Your Name and/or Pseudonym as an e-signature (or the name of the person you’ve authorized to submit this request, with a slash before it and after it):
Link(s) to the unauthorized works (link to the pdf, the mobi and the page hosting all of it): 
Link(s) to an authorized version of your work (whether on AO3, tumblr, LJ or somewhere else): 
An email address of the submitter (include it again even if it’s in the header): 
This statement: I have good faith belief that use of the material in the manner complained of is not authorized by the copyright owner, its agent, or the law.
This statement: The information in the notification is accurate, and under penalty of perjury, that the complaining party is authorized to act on behalf of the owner of an exclusive right that is allegedly infringed.

You may wish to submit the same content to Google via this page, or to BING via this page.  ADDED 4/14/15: You can also send it to Cloudflare, which hosts (we think?) ebooks-tree's site.

Alternative wording from Tumblr user besinaao3:

(according to OTW, AO3 and fuckyeahcopyright, “as a matter of law you do not need to include the legal name of the copyright claimant/the fanfic writer, but  you should include the pseudonym that the fic was posted under if you don’t want to include a legal name or address.”)

My name is [name] and I am the author and owner of the following works:
-        “Of Hunters and Wolves” by “Quicklikelight”
-        “In the Woods” by “Quicklikelight”
-        “This is a Gift” by “AnneinColor” Fill in appropriate titles/author names

These are my intellectual property. I do not give you or anyone else permission to offer these works for download, and I did not consent for them to be available on your website. I am requesting that you remove them immediately. I can be reached by e-mail at [e-mail].
This information is accurate, and under penalty of perjury, I am authorized to act on my own behalf as the owner of this material.

Signed,
[Name]