Iranian cyber attacks against U.S. financial institutions have resulted in false claims by U.S. officials and cybersecurity experts that the State of Iran was behind them. The fact is that while Iran is developing a capable cyber warfare division, the distributed denial of service attacks against U.S. banks have been part of a hacktivist protest organized by Izz ad-Din al-Qassam a.k.a Qassam Cyber Fighters called Operation Ababil. The group first announced its plans on September 18th 2012 on Pastebin.

Dear Muslim youths, Muslims Nations and are noblemen
When Arab nations rose against their corrupt regimes (those who support Zionist regime) at the other hand when, Crucify infidels are terrified and they are no more supporting human rights. United States of America with the help of Zionist Regime made a Sacrilegious movie insulting all the religions not only Islam.
All the Muslims worldwide must unify and Stand against the action, Muslims must do whatever is necessary to stop spreading this movie. We will attack them for this insult with all we have.
All the Muslim youths who are active in the Cyber world will attack to American and Zionist Web bases as much as needed such that they say that they are sorry about that insult.
We, Cyber fighters of Izz ad-din Al qassam will attack the Bank of America and New York Stock Exchange for the first step. These Targets are properties of American-Zionist Capitalists. This attack will be started today at 2 pm. GMT. This attack will continue till the Erasing of that nasty movie. Beware this attack can vary in type.
Down with modern infidels.

On September 19th, they expanded their financial targets to include JPMorganChase.

On September 25th, they posted another announcement to Pastebin (which has since been removed but can be read here) which stated that they’ll be expanding the attacks: