The cyber attacks against U.S. banks last month were more widespread than reported, industry experts say. Though JPMorgan Chase and BB&T were the first big banks to confirm denial-of-service attacks, roughly a half-dozen institutions endured digital assaults around the same time, according to Radware, a security firm that has investigated cyber intrusions on behalf of financial firms.

The initial attacks "were the largest attacks we've seen to date in scale," Carl Herberger, a vice president of security solutions at Radware, told American Banker, a sister publication to Bank Investment Consultant. "The one that was advertised to the world was Chase, but I can tell you that almost on an hourly basis banks were being attacked, which is a very substantial campaign."

"If you actually measure the response time of some of these banks that are being attacked, you can see that they are under duress," Herberger adds. "Most of them labored for hours on end with little or no response."

The attacks last month followed a threat earlier that same day by the al-Qassam Cyber Fighters, a group that has claimed responsibility for a series of incursions since September that have bogged down websites at some of the nation's biggest banks and prevented customers from accessing their accounts.

The group said it would continue its campaign against banks including JPMorgan Chase, Bank of America, Citibank, PNC Financial, Fifth Third Bancorp, Union Bank, BB&T, and Capital One, until YouTube took down a trailer for an anti-Muslim film.

Herberger declined to say which banks beside Chase weathered attacks in the recent wave last month, citing confidentiality agreements between Radware and its clients.

BB&T spokeswoman Merrie Tolbert said in an email to American Banker last month that the Winston-Salem, N.C., bank "experienced intermittent outages" but said the bank was able to restore service quickly.

Daniel Weidman, a spokesman for Union Bank, said in an email that the bank's website also "experienced intermittent outages" before resuming regular operation.

Citigroup, Fifth Third and Capital One spokespeople said their companies' websites functioned normally that day. Bank of America's websites also continued to operate without incident, according to a source close to the company.

"If you have a leak in a boat, you can build a bigger boat so the leaks won't mathematically sink your boat," Herberger says. "That's been fundamentally the process many folks have been taking. We see few instances of fixing the leak."

While banks continue to take steps to strengthen security, hackers continue to hone their capabilities and can outmatch banks' best efforts to deter them, experts say.

Hackers "are certainly more sophisticated; it's not the 14-year-old sitting on his dad's PC writing a virus," says Mike Whitt, BBVA Compass' chief information security officer. "This is a business for these guys, and it's really a business that runs in kind of parallel to the legitimate market, so the actors can be anyone from organized crime, to terrorist organizations, or even state-sponsored attacks."

According to Whitt, banks have an especially tough job because they are not security companies and have limited resources to devote to thwarting attacks, while attackers have "somewhat unlimited" resources "because most of the money that they are using is through ill-gotten gains."

If a bank needs hardware, it has to go through a process to get it approved. "If one of these bad guys needs a couple more PCs, they find PCs that are on the Internet and they take them over, own them, and then they have additional hardware resources," Whitt says.

Indeed, IT employees at banks are dealing with malicious coders at all ends. Depositories are being targeted by both denial-of-service attacks, in which botnets bombard a financial services company's website in order to shut it down and disrupt services to customers; and invasive malware that infects customers' sometimes insecure devices and compromises their accounts.

Often times, denial-of-service attacks "can be a diversion," says Dave Ostertag, a computer security expert and a global investigation manager with Verizon. At the same time, criminals might be trying to extract financial information from a bank using various techniques, he says.

There are, of course, prescriptions that banks can follow in order to block some fraudulent money transfers. For instance, Ostertag says that a bank could run all of its ACH payments on a single, dedicated computer that isn't handling any of a bank's employee email or web traffic.

Sergio Fidalgo, BBVA Compass' chief information officer, says his bank hedges against instances of high-tech theft by inserting people and processes into transactions. "There is not a single point of failure in which we rely on from a security perspective," he says. "It's not just about detecting, preventing and fighting the attacks... we have procedures that have to be strictly met when we talk about money leaving the bank."

Human beings, however, can only catch so much, says Barak Eilam, president of Israeli tech vendor NICE Systems for the Americas. Earlier this year, NICE launched a suite of services that employ biometric technology to screen calls and recognize voices in the case of such a scam.

Eilam stresses that though computers can only do so much, they certainly pare down what could be indomitable threats to banks by flagging suspicious activity. "Because of banks' scale, complexity, and sophistication ... this is where technology comes in place," Eilam says. "Technology helps."

Even then, people will always be susceptible to social engineering attacks in which hackers pick up just enough information about a person to fool a bank employee into moving a victim's money, or worse.

Still, as Herberger sees it, banks continue to play catch-up. "How is it we've gotten to the point where we've had the largest financial institutions, the most handsome security departments and all of the regulators, where there was a risk to begin with and numerous vulnerabilities that are exploitable, and yet we haven't been able to resolve it?"

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