Cybercriminals have built a cloud-based fraud system that targeted wealthy people and commercial accounts in bilking primarily European banks of possibly billions of dollars, security vendors say.The international ring targeted accounts with an average of $300,000 to $600,000, and attempted to transfer as much as $130,000 to bogus business accounts, Intel-owned McAfee said Tuesday. While McAfee did not know how much money was actually stolen, the vendor estimates that it ranged from $75 million to $2.5 billion.The ring targeted banks in Europe and then expanded to Latin America and more recently the United States, where it had just gotten started, Dave Marcus, director of advanced research and threat intelligence at McAfee Labs, said. McAfee, which investigated the ring's operation over the last six months with Guardian Analytics, is working with law enforcement agencies to shut down the fraudsters.What is unique about the fraud was the amount of automation used, a feat made possible through the use of cloud computing, Marcus said. The combination of remote servers and an intimate knowledge of banking transaction systems made it possible to automate the theft, rather than simply stealing user names and passwords and having someone manually transfer money from a computer."The automated nature of these attacks really require that kind of server\/cloud functionality," Marcus said. "It can't all take place on the host [computer]. All of the logic and all of the sophistication really does reside on that [cloud] server."McAfee first discovered the fraudsters operating in Italy, and later followed them to Germany, the Netherlands and other countries in Europe. In March, the ring was found operating in Colombia and one server was later traced to the United States. "It looks like it [the ring] just started making the transition to the U.S.," Marcus said.The fraud started with an email cleverly disguised to look like it came from the recipient's bank. Clicking on a link in the message downloaded the malware that would later use web-injects to steal the information needed to perform fund transfers. Web-injects are fake pages or form fields launched while a person is on an online banking site.\u00a0McAfee, which dubbed the investigation "Operation High Roller" because of the wealthy victims, found 60 servers processing thousands of attempted thefts. Most of the transfers were for less than $10,000, with the highest reaching $130,000.The fraudsters used common Zeus and SpyEye malware platforms as the base of the malicious code, which was customized for each targeted bank. Once the malware stole the needed information, transfers were performed via the control servers, which were even able to obtain the information needed to bypass smartcard readers often used in Europe for two-factor authentication. "We have not seen this level of sophistication before," Marcus said.Besides the use of the cloud, the fraudsters had an impressive knowledge of how banking transaction systems worked. McAfee wasn't able to determine how the criminals gained that level of understanding. "You can't make a fraudulent transaction look like a valid transaction, if you don't know what you're doing," Marcus said. "And these guys know what they're doing."