Anonymous

Anonymous (with reference to the site you provided)

Anonymous is a decentralized international movement of digital activists and hacktivists known for high-profile cyber operations against governments, corporations, and other institutions. It operates without a central leadership or formal membership, and participants (“Anons”) are often identified by the Guy Fawkes mask and by the refrain “We are Anonymous. We are Legion.” The group’s actions are driven by a broad, loosely coordinated set of causes rather than a unified agenda, and its members may join or leave at will. (britannica.com)

Regarding the specific website you cited (http%3A%2F%2Fbitcoinsgratis.tk%2Fgastar%2F): there is no clear, verifiable evidence that this site is an official or authoritative channel of Anonymous. Anonymous has no formal, centralized site or leadership, so attribution to a single URL should be treated with skepticism unless corroborated by credible sources. (britannica.com)