Washington: JP Morgan Chase and at least four other US banks have been victims of a "sophisticated" series of cyber attacks this month, sources close to the investigation told The New York Times.
Hackers gained access to large amounts of bank data, including information from the savings accounts of customers, the sources said.
The FBI is investigating the attack and seeking to determine whether its purpose was economic or part of an international espionage or intelligence operation.
"Companies of our size unfortunately experience cyber attacks nearly every day. We have multiple layers of defence to counteract any threats and constantly monitor fraud levels," JP Morgan spokeswoman Patricia Wexler said in a statement.
According to cyber security experts consulted by the newspaper, there is no evidence of any political motivation behind the attacks, nor has any connection with countries like Russia or Iran been established.
Recently, the US banking sector has been targeted by economically-motivated hackers.
But the fact that JP Morgan has not detected fraud after the latest attacks has led investigators to be open to all possibilities.
