Over the couple of weeks, many major banks in the U.S suffered day-long slowdowns and been sporadically unreachable for many customers. The attackers, who took aim at Bank of America first, went after their targets in sequence, reports CNNMoney's David Goldman.
Security experts say the outages stem from one of the biggest cyberattacks they've ever seen. These "denial of service" attacks - huge amounts of traffic directed at a website to make it crash - were the largest ever recorded by a wide margin, according to two researchers. A financial services industry security group raised the alert level to high in response to the attacks.
The Islamist group Izz ad-Din al-Qassam Cyber Fighters publicly claimed responsibility for the attacks in what it called "Operation Ababil," but researchers are divided about how seriously to take their claims. The group has launched attacks in the past, but those have been far less coordinated than the recent batch.
Sen. Joe Lieberman, an Independent from Connecticut, said in a C-SPAN interview on Wednesday that he believed the attacks were launched by Iran.
"I don't believe these were just hackers who were skilled enough to cause disruption of the websites," he said. "I think this was done by Iran ... and I believe it was a response to the increasingly strong economic sanctions that the United States and our European allies have put on Iranian financial institutions."
A cybersecurity firm following the attacks also expressed doubt about the connections between the Cyber Fighters and the bank attacks. On social networks and chat forums, the group urged its followers to use a mobile "low orbit ion cannon" - a software tool typically used by Anonymous and other hacktivist groups to direct a massive flood of traffic at a targeted site.