Hacker attacks continue to temporarily swamp the security systems of the biggest banks, and it's the volume of the attacks rather than the technology of the assailants that is breaching the banks' defenses, according to American Banker.

There is apparently no short-term solution to the problem, security experts say.

The unknown assailants claiming responsibility call themselves the “al-Qassam Cyber Fighters.” The group has vowed to continue until YouTube removes a trailer for an anti-Muslim film.

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"The attackers obviously have someone who's put a lot of money into infrastructure and these guys have the capability to launch attacks like the world has never seen before," said Dave Ostertag, a global investigation manager with Verizon.

In the first week of April, Wells Fargo’s online and mobile banking systems were inoperable for about six hours. Similar denial of service attacks hit JPMorgan Chase, BB&T, American Express and TD Bank recently.

American Banker said the massive volume of the attacks is unleashing a flood of data at websites with the goal of overwhelming them.

"Twelve months ago, the maximum protection for a major financial institution was 10 gigabytes per second," said Ostertag. "Now we're averaging 40 to 50 gigabytes per second. The entire industry has changed."

Ostertag said Verizon and other network operators have been able to blunt some attacks by redirecting suspicious traffic.

He declined to discuss where the current denial of service traffic that passes through Verizon’s network is emanating from, claiming the information is classified.

Avivah Litan, an analyst with Gartner Research, said the unknown group is believed to total about 25 people, but it is unclear who sponsors them. Some U.S. officials have charged the al-Qassam Cyber Fighters group is sponsored by the Iranian government, however.

Litan told American Banker that the current hacker strategy against U.S. banks involves targeting specific web pages, such as a help page or log in page, which can then be hit 20 million times a minute.

“It’s not hopeless, but it doesn’t look good for the next few months,” Litan said of the banks’ technology countermeasures. “There’s a lot of programming that needs to be done.”

Technology publisher Ars Technica said there is some concern by experts that criminals could use the denial-of-service attacks as a cover for fraudulent activity.

Dan Holden, director of Arbor Networks’ Security Engineering & Response Team, said he considered the criminal scenario unlikely, but that the current bank hacker wave appears to have serious financial backing.

The goal seems to be "mainly been around being able to attack multiple targets. They're not interested in the biggest [distributed denial of service] they can make — they're more interested in creating constant pressure to prove whatever they're trying to prove. They're in it for the long haul," Holden told Ars Technica.

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