Distributed denial-of-service (DDoS) attacks used by the hackers to hack banking websites successfully disrupted the operations of leading Wall Street financial institutions, including Bank of America, JPMorgan Chase, and Wells Fargo, as well as other firms in the beginning of the month. Last week, the attacks extended to include Capital One, SunTrust, and Regions Financial.

In spite of an advance warning by attackers, all of the targeted banks' websites still suffered disruptions.

A self-described hacking group, the “Cyber fighters of Izz ad-din Al qassam”, has taken credit for the attacks, and has also released statements denying that it's behind wire-transfer attacks that have been launched against U.S. banks over the past year. The group said the DDoS attacks are meant to protest the release of a clip from the "Innocence of Muslims" film that mocks the founder of Islam.

But information security experts have been finding inaccuracies in the Cyber fighters of Izz ad-din Al Qassam's statements, as well as evidence that the group is better organized than it has stated. Meanwhile, U.S. government officials have been stepping up their public accusations that the Iranian government has been directly sponsoring the attacks.

U.S. officials recently said that they've traced the attacks to a group of fewer than 100 Iranian information security specialists--based at Iranian universities and technology companies--who they say have been the actual hackers behind the bank attacks. The officials said that the evidence that conclusively links the Iranians to the attacks is classified, but said the scale and effectiveness of the DDoS attacks reinforced that the hackers had substantial backing.

Iranian officials have denied hacking any U.S. banks. But earlier this year, Iranian government officials announced the creation of a military "cyber corps" to help the country better defend itself against online attacks such as Stuxnet.

The U.S. government hasn't directly taken credit for creating Stuxnet, Flame, or other espionage Malware that was used against Iranian systems. But according to David Sanger's book Confront and Conceal: Obama's Secret Wars and Surprising Use of American Power, published earlier this year, White House officials--speaking off the record--said that the Malware had been developed as part of a classified program code-named "Olympic Games."