Bloomberg  [unpaywalled] – “FBI leaders have warned that they believe hackers who broke into AT&T Inc.’s system last year stole months of their agents’ call and text logs, setting off a race within the bureau to protect the identities of confidential informants, a document reviewed by Bloomberg News shows. FBI officials told agents across the country that details about their use on the telecom carrier’s network were believed to be among the billions of records stolen, according to the document and interviews with a current and a former law enforcement official. They asked not to be named to discuss sensitive information. Data from all FBI devices under the bureau’s AT&T service for public safety agencies were presumed taken, the document shows. The cache of hacked AT&T records didn’t reveal the substance of communications but, according to the document, could link investigators to their secret sources. The data was believed to include agents’ mobile phone numbers and the numbers with which they called and texted, the document shows. Records for calls and texts that weren’t on the AT&T network, such as through encrypted messaging apps, weren’t part of the stolen data. AT&T publicly disclosed the breach in July and said it included six months worth of mobile phone customer data from 2022. The hackers threatened to sell the data unless the telecommunications company paid an extortion fee. A person with knowledge of the breach, who reviewed a sample of the stolen information, confirmed that it contained records of sensitive FBI communications: the call logs of at least one agent. The person asked not to be named because the information is private. The FBI’s concern about the hack compromising its secret sources, which hasn’t been previously reported, highlights how data stolen from phone companies has the potential to disrupt criminal investigations and national security. Former agents said it also raises questions about the bureau’s own security practices and how it safeguards its sources. US authorities are still investigating a separate breach of nine telecommunications companies, including AT&T. They blamed Chinese state-backed hackers for those intrusions, which compromised the communications of a number of people in government and politics…”