An apparent wave of cyber attacks against major banks continued Wednesday, with U.S. Bancorp the latest to suffer disruption.

The lender's website,, started having "intermittent connectivity issues" around 8:30 a.m., and trouble continued through the day, said Tom Joyce, a spokesman for the Minneapolis-based bank. Pages have been slow to load, and some customers can't access the site at all, Joyce said, adding that the bank's IT staff was working hard to fix the problem.

Joyce described the disruptions as a "denial of service" attack similar to what other large U.S. banks, including Wells Fargo & Co., have experienced in the past week. He said the bank has no idea who is behind it.

Denial-of-service attacks are relatively unsophisticated actions, somewhat like an online flash mob aimed at disrupting websites with a lot of traffic.

"This is all related to unusual and coordinated high traffic volume designed to slow the system down," Joyce said in an interview.

Joyce said the bank is working closely with federal law enforcement officials on the matter. U.S. Bank customers' data and funds are secure, he said.

The technical attacks started last week at J.P. Morgan Chase & Co. and Bank of America Corp., and spread Tuesday to Wells Fargo.

Officials at San Francisco-based Wells Fargo, which has a large Minnesota presence, declined to discuss the problem beyond issuing a statement apologizing to customers.

"We are working quickly to resolve this issue," said Sara Hawkins, the bank's spokeswoman for technology and operations. "We constantly monitor the environment, assess potential threats, and take action as warranted."

Complaints about not being able to log on to the bank sites and other technical issues have piled up at the website A complaint about Wells Fargo posted there Wednesday morning said: "2nd day in a row! Come on already! Fix this!"

Theories vary as to who is behind the string of cyber attacks. Sen. Joe Lieberman, I-Conn., chairman of the Senate Homeland Security & Governmental Affairs Committee, said in a C-SPAN interview last week that he believes Iran is orchestrating the campaign.

"I don't believe that these were just hackers," Lieberman said in the interview. "I think that this was done by Iran and the Quds Force, which has its own developing cyber attack capacity. And I believe it was a response to the increasingly strong economic sanctions that the U.S. and our European allies have put on Iranian financial institutions."

Lieberman said it was "a theory, but I think it has a basis."

The Quds Force is an elite special operations unit of the Iranian military.

By contrast, an Islamic group calling itself Cyber fighters of Izz ad-din Al-qassam has posted notices on a website called claiming responsibility for the campaign. It says it is retaliating for the anti-Islam video on YouTube ridiculing the prophet Mohammed and says it will continue until the video is erased. The video has sparked deadly riots in the Middle East.

A Pastebin posting Tuesday afternoon warned that the group would attack for eight hours daily, and planned to hit U.S. Bank's website Wednesday and PNC on Thursday. A spokesman for Pittsburgh-based PNC Bank did not immediately return phone calls seeking comment.

Jennifer Bjorhus • 612-673-4683