The Los Angeles Times reported Wednesday that the Wells Fargo servers were so busy fending off a massive cyber attack that other bank services suffered from slowdowns and other glitches.
With an online posting a group named Izz al-Din al-Qassam Cyber Fighters claims responsibility for cyber attacks on Bank of America, Citi and JPMorgan Chase and said cyber attacks on banks would continue.
The group said it would target U.S. Bancorp Wednesday and PNCFinancial Thursday, the Times said.
"I wouldn't necessarily take at face value any of its claims about attribution," said Dmitri Alperovitch, co-founder of CrowdStrike Inc., a cyber security firm.
Alperovitch, however, said the posting online was "accurate in terms of predicting future attacks."
The posting demanded that a video insulting Islamic prophet Muhammad be taken off the Internet.
Wells Fargo, meanwhile, apologized for the inconvenience caused by the cyber attack.
"We apologize to customers who may be experiencing intermittent access issues to wellsfargo.com and online banking. We are working to quickly resolve this issue. Customers can still access their accounts through our ATMs, stores and by phone," the bank said in an email.