In short, to the U.S. government, anything anomalous is an Iranian conspiracy. Wired writes:
A slew of American officials have blamed Iran for attacks on the servers of Bank of America, Well Fargo, HSBC, and other western banks. But the hackers taking credit for the sophisticated distributed denial-of-service strikes say that’s all wrong; they claim they hit the financial institutions because they were pissed off about “The Innocence of Muslims,” the infamous viral video making fun of the Prophet Muhammad. Tehran didn’t have a thing to do with it.
“We are not dependent on any government. We merely wanted to protest against the insulting movie,” people claiming to be part of the Izz ad-Din al-Qassam Cyber Fighters [said].
Some security researchers believed the attacks to be so sophisticated, they could’ve only been pulled off with government help. ”This isn’t consistent with what hacktivists are capable of,” Michael Smith, a security specialist at Akamai, said in September. Pretty soon, American politicians starting blaming one government in particular: the one in Tehran. ”I think this was done by Iran and the Quds Force, which has its own developing cyber-attack capacity,” Sen. Joe Lieberman told C-Span around the same time.