The massive SolarWinds hack that breached the U.S. government and thousands of other public and private customers is “likely Russian in origin,” according to a joint statement released by the FBI, the Office of the Director of National Intelligence, the National Security Agency, and the Cybersecurity and Infrastructure Security Agency.

The agencies, which are supporting the National Security Council’s Cyber Unified Coordination Group task force, said on Tuesday that a likely Kremlin-backed advanced persistent threat actor “is responsible for most or all of the recently discovered, ongoing cyber compromises of both government and non-governmental networks.”