A little-known group called "Cyber fighters of Izz ad-din Al qassam" claimed credit for the attacks, but some security experts think a nation may have been behind the campaign because of the scale and organized nature of the attacks.

In mid-September, the Financial Services Information Sharing and Analysis Center (FS-ISAC) warned banks to be on guard against cyberattackers seeking to steal employee network login credentials to conduct extensive wire transfer fraud. Specifically, the alert warned banks to watch out for hackers using spam, phishing emails, Remote Access Trojans and keystroke loggers to try and pry loose bank employee usernames and passwords.

FS-ISAC also noted that the FBI had seen a new trend where cyber criminals use stolen bank employee credentials to transfer hundreds of thousands of dollars from customer accounts to overseas locations.

Over the past few years, cyber crooks have siphoned off millions of dollars from small businesses, school districts and local governments by stealing online usernames and passwords and using those credentials to make the transfers.

The latest discussion suggests that they now have individual consumer accounts in their crosshairs, Ahuvia said, warning that the gang plans to attempt to infiltrate computers in the U.S. with a little known Trojan malware program called Gozi Prinimalka.