The news site said the attack was described by one former US official familiar with the attacks as being "significant and ongoing" and looking to cause "functional and significant damage." Also, one source suggested the attacks were in response to US sanctions
on Iranian banks.
On Tuesday many customers discovered that access to the consumer banking website of Bank of America was unavailable, and JPMorgan Chase on Wednesday had the same problems, which multiple sources linked to a denial-of-service attack, in which a website is bogged down by a large number of requests.
A Chase spokesman said Wednesday that the consumer site was intermittently unavailable to some customers, but did not acknowledge then that there was an attack.
On Thursday, Chase said slowness continued but was resolved by late afternoon Eastern Time. Bank of America acknowledged on Tuesday that its site had experienced slowness, but would not say what caused it.
NBC explained that a group of hackers from the Middle East claimed responsibility for the cyber attack. In a statement published online the group explained that their actions came in response to the "Sacrilegious movie" that has caused riots throughout the Muslim world.
But a different source said this was just a cover story to hide the fact that the Iranian government is behind the attack.
Last week a financial services industry group, the Financial Services Information Sharing and Analysis Center, warned US banks, brokerages and insurers to be on heightened alert for cyber attacks.