FBI leaders have warned that hackers who breached AT&T's system last year likely stole months of agents' call and text logs, prompting an urgent effort to safeguard confidential informants' identities,

They believe hackers who broke into AT&T Inc.’s system last year stole months of their agents’ call and text logs.

Hackers who breached AT&T's systems may have handed criminals a roadmap to FBI informants, stealing call logs that could unravel investigations and jeopardize lives, according to alarming new details revealed Thursday.

FBI leaders have warned that hackers who breached AT&T’s system last year likely stole months of agents’ call and text logs, prompting an urgent effort to safeguard confidential informants’ identities,