Questions over who the hackers are and the approach of their attack concern government and industry officials. Also troubling is that about nine other financial institutions — a number that has not been previously reported — were also infiltrated by the same group of overseas hackers, according to people briefed on the matter. The hackers are thought to be operating from Russia and appear to have at least loose connections with officials of the Russian government, the people briefed on the matter said.
It is unclear whether the other intrusions, at banks and brokerage firms, were as deep as the one that JPMorgan disclosed on Thursday. The identities of the other institutions could not be immediately learned.
The breadth of the attacks — and the lack of clarity about whether it was an effort to steal from accounts or to demonstrate that the hackers could penetrate even the best-protected American financial institutions — has left Washington intelligence officials and policy makers far more concerned than they have let on publicly. Some American officials speculate that the breach was intended to send a message to Wall Street and the United States about the vulnerability of the digital network of one of the world's most important banking institutions.