The catastrophic hack of at least thousands of FBI officials’ personal data, including their addresses, phone numbers, and even their spouses, includes members of the FBI’s secretive hacking team, potentially revealing who exactly is in that unit, 404 Media has found.

The findings further highlight how sensitive the stolen data is, and how valuable it may be to criminals or to foreign intelligence agencies. There is very little public information about the FBI’s hacking unit, including the operations it conducts, the tools it uses, or which agents are part of it.

FBIjobs.gov offline on Wednesday as ShinyHunters group claims to have accessed records of agents and applicants

The FBI is investigating an apparent breach of its jobs website as a criminal hacking group claimed to have accessed “very sensitive data” on nearly all agents and job applicants.

“The FBI is aware of claims regarding unauthorized activity affecting FBIjobs.gov and is currently investigating,” the bureau said in a statement. The website, the main portal for prospective employees to learn about the FBI and initiate the application process, remained offline Wednesday morning.

A high profile hacking group claims it has breached multiple FBI-related services and stolen data “on all FBI employees and applicants.” A representative of the group, called ShinyHunters, told 404 Media the data includes FBI agents’ names, home addresses, phone number, and information on their spouse.

The data breach could be massively significant and may have all sorts of national security and counterintelligence implications. Criminals from the same ecosystem as ShinyHunters have previously used hacked data like phone records to track, intimidate, and harass the FBI agents investigating them. The highly sensitive data could also be a boon to foreign intelligence agencies who want to better understand how one of the most important law enforcement and intelligence agencies in the U.S. operates. And if the data fell into the hands of more criminals, FBI agents and their spouses could face serious threats to their safety.

“We hacked the FBI. We hold data on all FBI employees and applicants,” the representative of the group told 404 Media.