MILWAUKEE (WTAQ) - U.S. Bank is assuring its online customers that their accounts and personal information were not stolen in a cyber-attack.

Customers had trouble logging onto the bank’s Web site from mid-morning Wednesday until late in the afternoon.

U.S. Bank called it a “denial of service” attack, and it’s apparently a coordinated effort to slow down the Internet operations of the country’s biggest banks.

Spokesman Thomas Joyce said the worst thing that happened to customers was that they could not access their online accounts without trying a few times. He called it a coordinate volume of high traffic designed to slow down the system.

U.S. Bank, the former First Wisconsin, is now headquartered in Minneapolis. Citibank, JP Morgan Chase, and the Bank of America had similar attacks last week.

Wells Fargo Bank was hit Tuesday – and a group that claimed responsibility promised to hit PNC Bank Thursday. That company said it’s ready.

A posting on PasteBin.Com said the online bank attacks would continue until a video is taken off-line which insults the Islamic prophet Mohammed.

U.S. Senator Joe Liebermann of Connecticut says the bank attacks are supported by leaders in Iran, after U.S. sanctions were placed on that country due to its nuclear weapons’ program.