WASHINGTON — The Department of Homeland Security told employees on Thursday that it was aware of a “potential breach” and working to address the situation, a day after an activist group that publishes leaks released data on more than 41,000 workers at the department.

“The safety, security and privacy of our employees, officers, and their families remains a top priority,” Roman Jankowski, the department’s chief privacy officer, said in an email that was reviewed by The New York Times. “DHS leadership and component leaders are working to understand the scope of the situation, assess potential threats, and identify appropriate resources and protective measures.”

The organization behind the leak said it released identifying information about employees to promote transparency about the “key personnel” involved with the department’s deportation campaign, a pillar of President Donald Trump’s policy agenda.

The leak immediately raised concerns among workers who wanted to know how the department would help protect…