Current and former American officials described the intelligence breach as one of the worst in decades. It set off a scramble in Washington’s intelligence and law enforcement agencies to contain the fallout, but investigators were bitterly divided over the cause. Some were convinced that a mole within the C.I.A. had betrayed the United States. Others believed that the Chinese had hacked the covert system the C.I.A. used to communicate with its foreign sources. Years later, that debate remains unresolved.
