A hacking group cracked the U.S. Department of Homeland Security's personnel files, exposing the names, phone numbers and addresses of more than 40,000 DHS agents, operatives, and associates, on Wednesday, including those involved in undercover operations.

"On July 17th, Markwayne Mullin said he was 'turning up the heat.' This is what happens to ICE when you do that," a spokesperson for the hacktivist group behind the breach, the Department of Peace, said in an online statement.

The hackers said they stole the data by subverting DHS's single sign on system, according to an online post. It said it distributed that material to the group Distributed Denial of Secrets, which posted it online in a database called Icepick. The Department of Peace also shared the trove of data with Ryan Ottignon, a U.S.-based journalist, and a Swiss activist known as maia arson crimew. Together, the two created a searchable online database, with crimew doing all of the technical work, Ottignon told NPR.

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