“Until that very moment, we were unaware of this website even existing.”

Twente is hardly alone. Football Leaks did not exist until September, but it has made an undeniable impact in its nascent stage, publishing numerous documents intended to be kept secret, all with the intent of exposing the often murky world of soccer finances.

One European club official, speaking on condition of anonymity because he did not want to provoke the group, said, “No one knows exactly what is happening, but everyone knows that they don’t want to be next.”

Football Leaks is shrouded in mystery, and no one involved with it has offered any significant details about the identities of the organizers. Over the course of a lengthy email exchange with The New York Times, however, someone who identified himself as a leader of Football Leaks discussed the site’s background, its motivations and its intentions.

The organizers of the site are based in Portugal, according to the person, who asked to be referred to only as John. But, he said, they have used Russian servers and domains to store information “because it’s publicly known Russian authorities rarely cooperate with Western authorities.” The initial goal for the site, John said, was to highlight improprieties among Portuguese clubs, for whom the practice of third-party ownership, or T.P.O., has long been a common way for teams to purchase high-priced players without actually having all of the necessary funds themselves.