The FBI said in a statement Wednesday that it was working with the Secret Service to determine the scope of recent cyberattacks against "several American financial institutions." The agency did not name the companies that had been targeted.
Major U.S. banks said that they had been unaffected by the attacks.
Bank of America spokesman Dan Frahm said the bank had not seen any unusual activity regarding cyberattacks. Citigroup had no information to suggest that it was the victim of an attack, said a person familiar with the situation who spoke on condition of anonymity. Wells Fargo said in a statement that it had not been seen an impact from the attacks.
Banks face "thousands" of attempted attacks on their computer systems every day, though the majority of incidents remain unreported, said Avivah Litan, a cyber security expert at Gartner.
"There are lots of bad guys out there, continually probing bank networks, trying to get in," Litan said.
The perpetrators of the attacks range from financial hackers, who are typically based in Eastern Europe and Russia, to "hactivist" groups such as Anonymous, who are trying to make social and political statements, she said. Countries such as China also engage in cyberattacks in an attempt to steal intellectual property.
Customers who notice any suspicious activity on their accounts should contact the bank, said JPMorgan spokesman Michael Fusco. He also noted that JPMorgan customers are protected against losses from fraud.