JPMorgan Chase & Co is investigating a possible cyberattack and working with law enforcement to determine the scope, company spokeswoman Trish Wexler said.
The announcement comes after the FBI said Wednesday it's working with the Secret Service on the recently reported cyberattacks against several U.S. financial institutions.
Earlier, Bloomberg.com reported that Russian hackers attacked the U.S financial system this month, possibly in 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 the attack appeared "far beyond the capability of ordinary criminal hackers."
Additionally, the New York Times, citing people familiar with the matter, reported at least four other firms in addition to JPMorgan were hit this month by co-ordinated attacks that siphoned off huge amounts of data, including chequing and savings account information.
Wexler says JPMorgan is taking additional steps to safeguard sensitive or confidential information, though it not seeing unusual fraud activity at this time, she said.
JPMorgan is the largest bank in the U.S. by assets.
The FBI said in a statement that fighting cyber threats and criminals remains a top priority for the U.S. government, and it's "constantly working with American companies to fight cyberattacks."