The U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives said a cyberattack on a standalone computer system has been classified as a major incident under federal law. The agency notified Congress within the required timeframe. The system, separate from the ATF network, stored data on active investigations. A spokesperson said the breach did not affect the agency’s primary network. TechCrunch reported a claim of responsibility by the Qilin ransomware group on its leak site, without presenting evidence such as leaked data. Qilin operates a ransomware‑as‑a‑service model and has previously listed other organizations as targets. Under the law, major incidents are those likely to cause demonstrable harm to national security or U.S. interests, and agencies must report them to Congress within seven days. The ATF joins the U.S. Marshals Service, which disclosed a 2023 ransomware incident, and the FBI, which reported a 2026 breach exposing phone numbers of surveillance targets earlier this year.