A photo of police commander Jean-Baptiste Salvaing and his girlfriend Jessica Schneider was displayed at the French Interior Ministry in Paris, June 15, 2016.

French police investigating a woman for suspected ties to ISIS have made a chilling discovery, according to French police officials and prosecutors: The arrested woman had a USB drive that contained the personal details of thousands of French police officials.

That’s raised fears that a similar data breach may have helped an ISIS militant carry out the notorious June 2016 murder of a French police commander and his domestic partner, a civilian police employee.

The USB was discovered last October during raids on apartments and properties linked to the 25-year-old woman, who’s been identified publicly only as Mina B. She now stands accused of being in direct contact with an ISIS-directed group in the Belgian city of Verviers that was raided in January 2015. Two extremists were killed in that raid.

Phone intercepts linked Mina B. to the Verviers group, and police launched an investigation that culminated April 9 with charges that Mina B. had helped a friend leave France to join ISIS in Syria and Iraq. At that time, police also announced that they had discovered the USB drive in her apartment.

The USB drive, according to French investigators, had been partially erased. Reconstruction of some of the drive’s contents, however, recovered at least one personnel database, from 2008, that included a raft of details about police officers, including home addresses and vehicle information. Specialists are still trying to reconstruct the USB’s full contents.

“This is a disaster,” said one French police officer who works undercover on counterterrorism operations and cannot be identified.

The officer pointed out that while the restored database dates to 2008, “that’s only 10 years and many of the officers are still in service.”

He added, “The information contains all the information one needs to stalk and murder hundreds of police officers in their homes, which as you know has already happened.”

The officer was referring to the June 13, 2016, double murder of Jean-Baptiste Salvaing, a police commander in the Paris suburb of Les Mureaux, and his girlfriend, Jessica Schneider, 36, who was an administrative assistant in the police station at Mantes-la-Jolie, another Paris suburb. The accused killer was Larossi Abballa, who stabbed Salvaing several times outside the victims' home, before slitting Schneider's throat inside the home. He then streamed a statement supporting ISIS before French police shot him dead.