The No. 4 U.S. bank by assets and other large banks in recent weeks have suffered so-called denial of service attacks that delayed or disrupted services on customer websites. On Thursday, U.S. Defense Secretary Leon Panetta called the "scale and speed" of the attacks "unprecedented" in a speech that urged Congress and businesses to step up cybersecurity efforts.

Wells Fargo's Sloan told Reuters, "I don't want to minimize the potential damage it could cause to the industry."

"But in terms of how the industry performed and how Wells Fargo performed in reaction to the recent efforts we actually performed very well," he added.

Sloan said the bank continues to invest in its technology platform to defend against potential attacks. "We in the industry just have to appreciate it as a cost of doing business today," he said.

A group that calls itself the Cyber Fighters of Izz ad-din Al Qassam has claimed credit for the recent bank attacks, declaring them a protest against the anti-Islam video posted on YouTube and stoked violent protests across the Muslim world.

The hackers behind the attacks have used sophisticated and diverse tools that point to a carefully coordinated campaign, security researchers have told Reuters.

Sources familiar with the attacks have previously told Reuters that they could be part of a year-long cyber campaign waged by Iranian hackers against major U.S. financial institutions and other corporate entities.

Sloan declined to comment on the source of the attacks. Wells is in close contact with other banks and the federal government, he said. (Reporting By Rick Rothacker in Charlotte, North Carolina; additional reporting by Joseph Menn; Editing by Bernard Orr)

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