(Reuters) - Some U.S. Bancorp and PNC Financial Services customers were having trouble accessing the banks' websites on Wednesday, as U.S. financial institutions appear to be threatened by another round of cyber attacks.
Wells Fargo & Co also faced lingering problems with its website after customers had intermittent access issues on Tuesday, a spokeswoman for the bank said.
U.S. Bancorp is experiencing "unusual and high-traffic volume" on its site that is designed to slow down the system, bank spokesman Tom Joyce said. The problem is similar to what other banks have faced in the past week, he said.
"We are working closely with federal law enforcement officials to address this issue," he said. Customers data and funds are not at risk, he added.
A PNC spokesman said some if its customers may be experiencing difficulty logging into the bank's website on the first attempt. "We are aware of the situation and are working to restore full access," spokesman Fred Solomon said.
The attacks came after a posting on the Internet on Tuesday by an unknown person, calling for cyber attacks this week against Wells Fargo, U.S. Bancorp and PNC. A similar posting last week warned of attacks against Bank of America Corp and the New York Stock Exchange.
The person who posted the message on a site called pastebin.com said the attacks will continue until the film that had stirred anti-U.S. protests across the Middle East was removed from the Internet.
"Obviously, it looks coordinated," said Jeff Herdell, founder of a website called Sitedown.co, which has been tracking customer complaints about the banks' websites.
So-called denial-of-service campaigns are among the oldest types of cyber attacks and do not require highly skilled computer programmers or advanced expertise, compared with sophisticated and destructive weapons like Stuxnet, a virus widely believed to have been developed by the United States to damage Iran's nuclear program.
But the attacks can still be disruptive: If a bank's website is repeatedly shut down, the attacks can hurt its reputation, affect customer retention and cause revenue losses as customers cannot open accounts or conduct other business.
The attacks also cost banks because they have to add staff to handle phone calls and pay for additional network bandwidth.
Senator Joseph Lieberman, chairman of the Senate's Homeland Security and Governmental Affairs Committee, said on Friday that he believes Iran was behind the attacks.
"I think this was done by Iran and the Quds Force, which has its own developing cyber attack capability," Lieberman said during a taping of C-SPAN's "Newsmakers" program. The Quds Force is a covert arm of Iran's Revolutionary Guards.
Reuters reported on Friday that Iranian hackers have repeatedly attacked Bank of America, JPMorgan Chase & Co and Citigroup Inc over the past year as part of a broad cyber campaign targeting the United States.
The attacks, which began in late 2011 and escalated this year, have primarily been "denial of service" campaigns that disrupted the banks' websites and corporate networks by overwhelming them with incoming web traffic, said sources.
Reporting By Rick Rothacker in Charlotte, North Carolina; Editing by Bernard Orr