The leak website Distributed Denial of Secrets said on Wednesday it has released data on more than 40,000 U.S. Department of Homeland Security (DHS) employees, including details about officials working in sensitive fields such as surveillance and human intelligence.

DHS said in a statement it was "aware of a potential breach and is actively working to address the situation swiftly and effectively." The agency said it was working to ensure its employees were properly protected and would update the public "when more information is available.”The disclosure — which the non-profit data transparency group says draws on information obtained by an entity calling itself "Department of Peace" — is the third major government data leak to have made headlines in the past month.

In September, the hacking group ShinyHunters claimed the theft of a massive trove of data from the Federal Bureau of Investigation (FBI), including sensitive job details and medical information from thousands of bureau employees. Last week, the U.S. War Department was hit with a class-action lawsuit following a breach that exposed data on millions of current and former military personnel.

ShinyHunters hackers say they won't leak sensitive FBI data Dutch police arrest security professional in ShinyHunters investigation The DHS data includes names, phone numbers and email addresses of employees from Immigration and Customs Enforcement, Customs and Border Protection, Homeland Security Investigations, the Cybersecurity and Infrastructure Security Agency, and other DHS component agencies.

Also included in the data were job titles and email groups, which, among other details, showed which agents were assigned to special operations, surveillance jobs, computer forensics and undercover work.

In a statement, Distributed Denial of Secrets co-founder Emma Best said the hacktivist known as "maia arson crimew" developed a search tool for the data that would allow the public to browse it. Best said the tool would "replace anonymity with accountability" and empower journalists, guide public records requests and boost congressional oversight.

The Department of Peace did not immediately respond to a request for comment, but in a statement included with the data it said that DHS employees "have our information, so it's only fair that we have theirs" and that it hoped the data "can be used to limit further harm by the DHS and supports all efforts in that direction." The Department of Peace in March claimed responsibility for hacking DHS and posting documents related to contracts with outside vendors.

Best's statement said the Department of Peace harvested the data from the Okta sign-on service used by DHS. Reuters could not immediately corroborate the claim. Okta said in response to a Reuters query: "Okta is secure, and we have no evidence our data or systems were compromised." Reuters could not immediately verify the authenticity of the entire data trove but it was able to match personal information about six DHS employees named in the leak to credit bureau records and breach data carried by the dark web intelligence platform District 4 Labs.

Reuters called three DHS employees directly and was able to confirm their phone numbers and other details. One said it was the first they had heard of a breach.

In several cases, the data tracked information available on DHS employees' LinkedIn profiles. But in others, the data revealed non-public data about internal DHS organization charts or previously undisclosed programs or operations.