The information of potentially tens of thousands of former and current F.B.I. employees may have been compromised in a breach by the criminal hacking group known as ShinyHunters.
In a social media post on Tuesday, the F.B.I.’s director, Kash Patel, said the bureau was pursuing leads after an arrest of a person believed to have ties to ShinyHunters.
A criminal hacking group known as ShinyHunters said it had targeted the F.B.I. as retribution for its public warning in the spring that the group was known to harass its victims and their family members.