The Department of Homeland Security is investigating a cyber incident on its Homeland Security Information Network (HSIN). The breach, detected in late May and early June, may have exposed information shared among federal, state, local and law enforcement agencies. HSIN enables agencies to share intelligence and coordinate emergency responses. It was used during the World Cup events in the United States. The platform also managed the response to a 2023 mid‑air collision of an American Airlines jet and a U.S. Army helicopter over Washington, D.C., which killed 67 people. Nextgov and Bleeping Computer reported that attackers accessed HSIN servers in late May and early June. An unnamed DHS spokesperson said the department is aware of the incident, isolated the affected systems, mitigated the vulnerability and began a comprehensive forensic investigation. The investigation is ongoing and no further comment has been provided. It is unclear what data was stolen or how much was taken. Homeland Security did not respond to inquiries about the incident. Senator Mark Warner, the ranking member of the Senate Intelligence Committee, said the information shared on HSIN is highly sensitive and its exposure could threaten national security. The identity, affiliation and motives of the attackers remain unknown. Since the Trump administration took office in January 2025, the federal government has experienced several cybersecurity breaches. These include the sharing of classified information via unapproved messaging apps, the unauthorized access to personal databases by members of the Department of Government Efficiency, and a public disclosure of credentials by a CISA contractor that exposed access to government cloud systems. Earlier this year, the FBI notified congressional leaders that it had declared a significant cyber incident after exposing the phone numbers of surveillance targets. The investigation into the HSIN breach continues, and DHS has not released details about any data loss.