For me, this sounds like a real file that's flooded with fakes. The users will download a few KB, then get a "File Mismatch" error, because the fake flooders send the user invalid bits of the file. But it could also be something completely unrelated to that.
What you should do is to search for the hash of the file, and look at the results you get. see if it is a mixture of reals and fakes