(Reuters) -FBI leaders have warned that hackers who breached AT&T (NYSE:T)'s system last year likely stole months of agents' call and text logs, prompting an urgent effort to safeguard confidential informants' identities, Bloomberg News reported on Thursday.
The breach, believed to have compromised all FBI devices using the bureau's AT&T public safety service, included agents' mobile phone numbers and the numbers they used to call and text, according to a document reviewed by Bloomberg and its interviews with a current and a former law enforcement official.
Last July, AT&T said that the company suffered a massive hacking incident as data from about 109 million customer accounts containing records of calls and texts from 2022 was illegally downloaded in April.
FBI officials informed agents nationwide that details about their use on the telecom carrier's network were likely among billions of records stolen, the report said, adding that while the hacked records did not expose the content of communications, they could link investigators to their secret sources, the report added.
An FBI spokesperson told Reuters that the agency "has a solemn responsibility to protect the identity and safety of confidential human sources, who provide information every day that keeps the American people safe, often at risk to themselves."
In a subsequent message, the spokesperson said the FBI has a responsibility to protect the identity of "any individual who contacts the FBI and provides information."
AT&T spokesperson Alex Byers told Reuters that after "criminals stole customer data last year, we worked closely with law enforcement to mitigate impact to government operations."
The breach follows broader concerns about cyber-espionage targeting U.S. telecom networks. On Jan. 10, U.S. national security adviser Jake Sullivan said that the U.S. had taken steps in response to Chinese-linked cyber-espionage operations against U.S. telecoms firms.
U.S. telecoms firms Verizon (NYSE:VZ) and AT&T said late last year their networks had been targeted by the cyber hackers, but were now secure as they worked with the U.S. government and law enforcement.