Data identifying more than 41,000 employees and contractors for the US Department of Homeland Security (DHS) was released on Wednesday in an unprecedented leak that reveals how the agency is organized. The records, which were made public by the transparency nonprofit Distributed Denial of Secrets, reference operation names, surveillance programs and information on undercover initiatives.

DHS did not immediately return a message seeking comment.

The leaked data unveils the ​names, phone numbers and email addresses of employees from various DHS agencies, including Immigration ‌and Customs Enforcement, Customs and Border ‌Protection, Homeland Security Investigations, the Cybersecurity and Infrastructure Security Agency.

Most of the agents in the leak – more than 21,000 – work for CBP, and about 6,600 work for ICE.

The data also includes job titles, email groups and other details that show which agents were assigned to special operations, surveillance jobs, computer forensics and undercover work.

It was…