Launched from the middle east, hatching right now. Citigroup, bank of america, wells fargo, u.S. Bank corp and today, pnc. America's biggest banks, with millions of american families locked out of... See More
Launched from the middle east, hatching right now. Citigroup, bank of america, wells fargo, u.S. Bank corp and today, pnc. America's biggest banks, with millions of american families locked out of their accounts online. So, what does it mean for your money? Who is behind it? How long has it been happening? Officials across the government are tracking the attacks, working to keep them from becoming financial nightmares. Abc's gene your justice correspondent pierre thomas starts us off. Reporter: Tonight, the financial and banking industry is on high alert as a massive cyber attack remains under way. Potentially millions of customers trying bank online this past week blocked. Among the targets, bank of america, pnc, and wells fargo. There is an elevated level of threat. The treat level is now high. Reporter: Sources tell abc news it is a denial of service attack, where hackers from the middle east have secretly commandeered thousands of computers worldwide. Those computers, or zombies, have overwhelmed bank websites with a barrage of electronic traffic. Different banks have been targeted different days. Today was pnc's turn. We tried for three hours to get on pnc's website, but we couldn't get through. On facebook today, frustrated customers. Cynthia wrote, "trying to pay bills. This is ridiculous." Stacy posted, "hopefully it can be up soon. Never realized how dependent i am on it." A group of hackers calling themselves izz ad din al qassam warned the financial industry it was going to attack in retaliation for that controversial film that sparked outrage in the muslim world. The scary thing is that even with the warning -- the attack could be stopped. The u.S. Suspects hackers in iran may be involved. This is the first time that we know about, where a middle eastern entity, perhaps a middle eastern government, has attacks websites of critical inf infrastructure in the united states. Reporter: The hackers have not been able to steal any money in these attacks or disrupt financial markets, but authorities fear the next generation of wide scale cyber assaults could be far more devastating. And if they get inside the banks, they can move money around and cause financial chaos. So, pierre, the hackers are blanketing the banks with these attacks, but so far, everyone's money is safe. Reporter: That's right, george. To be clear, no money has been stolen yet. But many people trying to bank online could not for a time get access to their accounts. You can see how that could make it difficult for a small business. So, that's why tonight, the government is working so hard to locate and block those ongoing attacks.
This transcript has been automatically generated and may not be 100% accurate.