So far, the only named target is JPMorgan Chase & Co. but, according to the NYT, at least four more banks have been hit.
The attackers managed to exfiltrate gigabytes of sensitive data such as customers' checking and savings account information.
According to Bloomberg, in one specific case the attackers took advantage of a zero day vulnerability to gain a foothold in the company's systems. A similar zero day was recently used in attacks against European banks.
It's still unknown who might be behind the attacks. Some security experts say that their sophistication may point to state-sponsored hackers, and there have been speculations that Russian hackers might be the culprits, possibly launching the attacks as a form of retaliation for the economic sanctions directed against Russia in the wake of the escalation of conflict in Ukraine.
It's also possible that, at least in JPMorgan's case, the attack has been partially motivated by revenge as earlier this year the bank has blocked a payment from a Russian embassy to the affiliate of a US-sanctioned bank.
Since attacks against the US and European banking sector have increased in the last few months, it's also entirely possible that these attacks are just a continuation of previous ones, and might be aimed at collecting information that can later be misused to steal money.
“Companies of our size unfortunately experience cyber attacks nearly every day,” a JPMorgan spokeswoman commented. “We have multiple layers of defense to counteract any threats and constantly monitor fraud levels.”
But, it seems that even this is not enough when faced with determined attackers.