A report on Bloomberg.com said Wednesday that the FBI is investigating an incident in which Russian hackers attacked the U.S financial system this month in possible retaliation against U.S. government-sponsored sanctions aimed at Russia.
The attack, Bloomberg said, led to the loss of sensitive data. Bloomberg cited security experts saying that the attack appeared "far beyond the capability of ordinary criminal hackers."
The New York Times, citing people familiar with the matter, said JPMorgan Chase and at least four other firms were hit this month by co-ordinated attacks that siphoned off huge amounts of data, including checking and savings account information.
JPMorgan spokeswoman Trish Wexler said large companies experience cyberattacks nearly every day.
"We have multiple layers of defence to counteract any threats and constantly monitor fraud levels," said Wexler, who did not confirm the reports.
The Wall Street Journal cited unnamed sources in a report that called the attacks a "significant breach of corporate computer security."
JPMorgan is the largest U.S. bank by assets.
The FBI said in a statement that combating cyberthreats and criminals remains a top priority for the U.S. government and that it's "constantly working with American companies to fight cyber attacks."