US Bank acknowledged Thursday its website was the target of "attacks" aimed at disrupting its system but that customer data and financial information were not compromised.
The eighth largest US banking firm said it was hit by a denial-of-service attack, which came after a threat against US financial companies from a group pledging retaliation for an online video that has sparked unrest in the Muslim world.
"The attacks yesterday involved unusual and coordinated high traffic volume designed to slow down the system. Customer personal and financial information were not compromised," said a statement from Nicole Garrison-Sprenger at the holding company US Bancorp.
The statement said the attacks caused "intermittent delays" but did not take down the company's website or mobile application.
"Our systems are performing well today, but we are continuing to monitor the situation and take any precautions we deem necessary," she said. "We are working closely with federal law enforcement officials."
PNC Bank, another firm mentioned in the threat, said its site was experiencing problems on Thursday, but did not elaborate.
"Some customers may experience difficulty logging in on the first attempt, but in general, customers have access to their accounts," a statement from the bank said.
"PNC has taken appropriate action to maintain customer service in response to the difficulty experienced by other banks over the past two weeks."
Wells Fargo's website was experiencing problems Tuesday and Wednesday.
The problems arose after a group calling itself "Cyber fighters of Izz ad-din Al qassam" announced that three banks would be targeted for the second week of "Operation Ababil."
The Site Intelligence Group, which monitors threats from the so-called "global jihadist network," said the group had posted a message warning against attacks on Wells Fargo on Tuesday, US Bank on Wednesday and PNC Bank on Thursday.
Last week, the "cyber fighters" group said it launched attacks under the name "Operation Ababil," meaning "Swarm," against the websites of Bank of America and the New York Stock Exchange on September 18, and Chase on September 19.
A US financial industry group warned banks and other institutions to brace for potential cyber attacks following last week's message.
The Financial Services Information Sharing and Analysis Center said it raised its cyber threat level from "elevated" to "high."
The group, which monitors cyber threats to the sector, cited "recent credible intelligence regarding the potential for DDoS (Distributed Denial of Service) and other cyber attacks against financial institutions."